Curing systems for materials that consume carbon dioxide and method of use thereof

ABSTRACT

The invention provides a curing system that is useful for curing materials that consume carbon dioxide as a reagent. The system has a curing chamber that contains the material to be cured and a gas that contains carbon dioxide. The system includes apparatus that can deliver carbon dioxide to displace ambient air upon loading the system, that can provide carbon dioxide as it is needed and as it is consumed, that can control carbon dioxide concentration, temperature and humidity in the curing chamber during the curing cycle and that can record and display to a user the variables that occur during the curing process.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of U.S. provisionalpatent application Ser. No. 61/785,226, filed Mar. 14, 2013, whichapplication is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The invention generally relates to systems and methods for preparingnovel composite materials. More particularly, the invention relates toequipment and methods used for making synthetic materials from a varietyof commonly available raw (or precursor) materials including water andcarbon dioxide. These composite materials are suitable for a variety ofuses in construction, infrastructure, art and decoration.

BACKGROUND OF THE INVENTION Concrete and Stone Materials

Humans have known and used concrete and stone since ancient times. Forexample, materials such as concrete, slate, granite and marble are usedin constructing various useful structures.

Concrete has been used for all manner of structures, including roads,buildings and building components such as pipe, block, pavers, andrailroad ties. Concrete has many beneficial properties such as beinghard (or resistant to deformation by mechanical forces), fireproof,water repellent, and resistant to the elements including resistance tomold growth and fungus growth.

Slate is a fine grained, metamorphic rock composed primarily of quartzand mica (sometimes formulated as KAl₂(AlSi₃O₁₀)). Because slate isplanar, hard, fireproof, water repellent, and resistant to the elementsincluding resistance to mold growth and fungus growth, it finds broaduses in building and construction, such as paver and roofing materials.Slate occurs in a variety of colors, for example, grey (pale to dark),green, cyan (bluish-green) or purple colors. Slate is generally“foliated”, or layered, such that it cleaves to give distinctive, planarsurface patterns. Its unique aesthetic and physical qualities have madeslate a desirable material in building and construction as well as indecorative art and sculpture.

Artificial slate-like materials have been studied in efforts to replacethe more expensive and scarce natural slate with low-cost, readilyproduced mimics. Such efforts, however, have yet to produce in asynthetic material that possesses the desired appearance, texture,density, hardness, porosity and other aesthetics characteristic of slatewhile at the same can be manufactured in large quantities at low costwith minimal environmental impact.

“Composite slate” is a simulated slate replacement made from recycledrubber and plastic. While these products resemble slate in appearanceand in some properties (primarily that they are water repellent andresist the elements), they lack slate's hardness, they are not fireproofto the extent that slate is fireproof, and they have a distinctlydifferent “feel”. Up close, they look different. Finally, although theymay contain recycled materials, they are based on materials derived frompetrochemical products.

Laminated asphalt sheets have the artificial look that has made themconsiderably less desirable than the natural slate. Other artificialslate mimics are prepared with a synthetic resin binder. These methodssuffer from a number of deficiencies, including poor reproducibility,low yield, deterioration, high finishing costs, unsatisfactorymechanical properties, and the like.

Granite is an igneous rock comprising principally quartz, mica andfeldspar. It usually has coarse grains within a fine-grained matrix. Itis known to occur in nature with various coloration.

Humans have known and used granite since ancient times. Its uniqueaesthetic and physical qualities have made granite a desirable materialin building and construction as well as in decorative art and sculpture.Artificial granite-like materials have been studied in efforts toreplace the expensive and scarce material with low-cost, readilyproduced mimics. Such efforts, however, have yet to produce in asynthetic material that possesses the desired appearance, texture,density, hardness, porosity and other aesthetics characteristic ofgranite while at the same can be manufactured in large quantities at lowcost with minimal environmental impact.

Most artificial granite mimics are prepared by blending natural stonepowder and minerals with a synthetic resin (e.g., acrylic, unsaturatedpolyester, epoxy). These methods suffer from a number of deficiencies,including poor reproducibility, low yield, deterioration, high finishingcosts, unsatisfactory mechanical properties, and the like.

Humans have known and used marble since ancient times. Its uniqueaesthetic and physical qualities have made marble a desirable materialin building and construction as well as in decorative art and sculpture.Artificial marble-like materials have been studied in efforts to replacethe expensive and scarce material with low-cost, readily producedmimics. Such efforts, however, have yet to produce in a syntheticmaterial that possesses the desired appearance, texture, density,hardness, porosity and other aesthetics characteristic of marble whileat the same can be manufactured in large quantities at low cost withminimal environmental impact.

Most artificial marble mimics are prepared by blending natural stonepowder and minerals with a synthetic resin (e.g., acrylic, unsaturatedpolyester, epoxy). These methods suffer from a number of deficiencies,including poor reproducibility, low yield, high finishing costs,deterioration, unsatisfactory mechanical properties, and the like.

Conventional Concrete Curing Chambers

Traditional concrete curing chambers are employed in a variety ofprecast concrete industries. A curing chamber is a fully or partiallyenclosed volume within which a controlled environment can be created.The enclosed volume may defined by the solid walls of a rigid structuresuch as a room or by a flexible barrier such as a tarp in the form of atent. After a concrete specimen is formed, it is placed in a controlledenvironment with sufficient moisture content and high enough temperatureto ensure that adequate curing is reached in reasonable times, typicallymeasured in days. Curing is vital to the quality of the concreteproducts and has a strong influence on properties such as durability,strength and abrasion resistance. Proper curing also aids to mitigatesecondary reactions that occur over time that may cause defects andunwanted color changes of the finished products.

Curing of concrete aids the chemical reaction of Portland cementconcrete known as hydration. The chamber is intended to keep thecontrolled environment conditioned and to maintain proper moisturewithin the product for the duration of the curing process. Anyappreciable loss of moisture will significantly delay or preventhydration and therefore decrease the properties of the product. Also,temperature plays a critical role during the curing process astemperatures below 10 C or above 70 C are highly unfavorable for curingwhile a temperature of 60 C is optimum.

Some companies that produce precast concrete attempt simplified curingprocesses using large rooms or areas covered by tarps which house theproducts in an attempt to maintain temperature and humidity. Thesesystems may act as a means to retain heat generated from the samples asa result of the exothermic reaction that occurs during the hydrationreaction or to retain heat or humidity that may be provided by externalheaters or water spraying systems. The most efficient and effectivemethod to cure precast concretes, however, relies on a permanent, sealedand controllable curing environment.

Several companies exist that specialize in the design, manufacturing,and installation of Portland cement concrete curing chambers for theprecast industry in the production of a wide range of products includedbut not limited to paving stones, concrete masonry units (CMU's),retaining walls, and roofing tiles. These curing systems are most oftenconstructed of steel, typically galvanized steel, and are insulated toprevent heat loss and maintain energy efficiency. Some systems arehighly automated and include “finger cars” which are automated transfersystems that take the formed precast products from the former into thecuring chamber racks. Commercial curing systems can range from the sizeof a standard shipping container (approximately 40 ft×10 ft×8 ft) allthe way up to high volume production systems that could be as large as200 ft λ100 ft×50 ft. The chambers can be configured as one “Big Room”system if the product is consistent, but for manufacturers with manyproducts lines a “Multi Lane” system is usually employed that allows forseparate temperature and humidity profile control of each individual baythat may be home to a different product line.

FIG. 1 is a schematic diagram of a traditional (prior art) concretecuring chamber, including the primary components which are a circulationsystem, a heat exchanger, and a humidification system. The system maycontain one or many blowers for gas circulation that provide high enoughgas velocities across the products to allow for distribution oftemperature and humidity as required. The heat exchanger can employ adirect gas fired burner, an indirect gas fired burner, or an electricheater. The humidification system usually includes atomizing spraynozzles or a heated vapor generator to provide water vapor to thesystem. Both temperature and humidity are monitored by sensors that sendsignals back to a computer or programmable logic controller that is usedto control the curing parameters. Many systems allow for completesequenced automation with temperature and humidity ramp up, dwell, andcool down steps such as are shown in FIG. 2 FIG. 2 is a graph thatillustrates a traditional (prior art) concrete curing profile showingtemperature as a function of time.

Treatment Systems Using Carbon Dioxide

Among the descriptions of systems that use carbon dioxide as a reactantare:

Kraft Energy, which describes their use in a number of documents such asKraft Energy Concrete Curing Systems. Kraft Energy at page 195 statesthat carbonation (of concrete) is “[a] process by which carbon dioxidefrom the air penetrates the concrete and reacts with the hydroxides,such as calcium hydroxide, to form carbonates. In the reaction withcalcium hydroxide, calcium carbonate is formed.” At page 37, KraftEnergy shows an illustration of a paver stone that has been carbonated.The caption under the image states “Typical carbonation found aftervapor curing a 7 N/mm2 solid block for 24 hours. (Phenolphthaleinindication).” The image shows a rectangular block that has a grey regionon its surfaces, and a purple center region. It is known thatphenolphthalein is a chemical compound with the formula C₂₀H₁₄O₄. Itturns colorless in acidic solutions and pink in basic solutions. If theconcentration of indicator is particularly strong, it can appear purple.As is evident from the image, the carbonation only proceeds to a shallowdepth and does not occur in the central portion of the block.

Also known in the prior art is Murray, U.S. Pat. No. 4,117,060, issuedSep. 26, 1978, which is said to disclose a method and apparatus isprovided for the manufacture of products of concrete or likeconstruction, in which a mixture of calcareous cementitious bindersubstance, such as cement, an aggregate, a vinyl acetatedibutyl maleatecopolymer, and an amount of water sufficient to make a relatively drymix is compressed into the desired configuration in a mold, and with themixture being exposed to carbon dioxide gas in the mold, prior to thecompression taking place, such that the carbon dioxide gas reacts withthe ingredients to provide a hardened product in an accelerated state ofcure having excellent physical properties.

Also known in the prior art is Malinowski, U.S. Pat. No. 4,362,679,issued Dec. 7, 1982, which is said to disclose a method of castingdifferent types of concrete products without the need of using a curingchamber or an autoclave the concrete subsequent to mixing, is casted andexternally and/or internally subjected to a vacuum treatment to have itde-watered and compacted. Then carbon-dioxide gas is supplied to themass while maintaining a sub- or under-pressure in a manner such thatthe gas-as a result of the sub-pressure-diffuses into the capillariesformed in the concrete mass, to quickly harden the mass. In oneembodiment (cf. FIG. 2)—in which the mass (I) is de-watered andcompacted by means of a mat or plate (2) placed thereupon and exposed toa sub-pressure via a pipe or a line (5)—the carbon-dioxide gas issupplied (through line 6) via said mat or plate (2) while using theunder-pressure prevailing in the mass. In another embodiment (cf. FIG.3) the sub-pressure is applied (via line 5) from one or more sides (2 b)of the mould to the interior of the element being cast, either by meansof special inserts, by holes or cavities inside the element or via aporous material layer (Ib) in the inner portion thereof. Then thecarbon-dioxide gas is supplied correspondingly (via line 6). These twomain embodiments may in certain cases be combined in different ways.Further the concrete may at the same time or subsequently be subjectedto another type of treatment such as impregnation by a suitablesolution.

Also known in the prior art is Getson, U.S. Pat. No. 4,862,827, issuedSep. 5, 1989, which is said to disclose at column 3, lines 26-32, that“Referring to FIG. 1, there is shown air intake 33 and exhaust 37, withchamber 35 downstream of the air path from air intake 33. This chambermay be used for introducing carbon dioxide for accelerating and curingcertain compositions and/or it may be used for introducing 30 additionalmoisture to further accelerate curing of moisture-curable systems.”

Also known in the prior art is Charlebois, U.S. Pat. No. 5,800,752,issued Sep. 1, 1998, which is said to disclose polymer compositeproducts, including products made of polymer concrete, reinforcedpolymer concrete and reinforced plastics, such as bulk:molding compound,sheet molding compound, mineral molding compound and advanced moldingcompound systems, are produced by the simultaneous application ofvibration, heat and pressure to a mixture of filler and polymericbinder. The simultaneous application of vibration, heat and pressureprovides a protective layer of polymerized binder that protects thesurfaces of the mold and provides products that are substantially freeof curling, cracking or voids. The process of the present inventionsubstantially reduces the time required to cure polymer compositeproducts.

Also known in the prior art is Soroushian et al., U.S. Pat. No.5,935,317, issued Aug. 10, 1999, which is said to disclose a CO₂pre-curing period is used prior to accelerated (steam or high-pressuresteam) curing of cement and concrete products in order to: (1) preparethe products to withstand the high temperature and vapor pressure in theaccelerated curing environment without microcracking and damage; and (2)incorporate the advantages of carbonation reactions in terms ofdimensional stability, chemical stability, increased strength andhardness, and improved abrasion resistance into cement and concreteproducts without substantially modifying the conventional procedures ofaccelerated curing. Depending on the moisture content of the product,the invention may accomplish CO₂ pre-curing by first drying the product(e.g. at slightly elevated temperature) and then expose it to a carbondioxide-rich environment. Vigorous reactions of cement paste in thepresence of carbon dioxide provide the products with enhanced strength,integrity and chemical and dimensional stability in a relatively shorttime period. Subsequent accelerated curing, even at reduced time periods(with less energy and cost consumptions) would produce higherperformance characteristics than achievable with the conventionalpre-setting period followed by accelerated curing of cement and concreteproducts.

Also known in the prior art is Ramme et al., U.S. Pat. No. 7,390,444,issued Jun. 24, 2008, which is said to disclose a process forsequestering carbon dioxide from the flue gas emitted from a combustionchamber is disclosed. In the process, a foam including a foaming agentand the flue gas is formed, and the foam is added to a mixture includinga cementitious material (e.g., fly ash) and water to form a foamedmixture. Thereafter, the foamed mixture is allowed to set, preferably toa controlled low-strength material having a compressive strength of 1200psi or less. The carbon dioxide in the flue gas and waste heat reactswith hydration products in the controlled low-strength material toincrease strength. In this process, the carbon dioxide is sequestered.The CLSM can be crushed or pelletized to form a lightweight aggregatewith properties similar to the naturally occurring mineral, pumice.

Also known in the prior art is CARBONCURE TECHNOLOGIES INC.,International Patent Application Publication No. WO 2012/079173 A1,published 21 Jun. 2012, which is said to disclose concrete articles,including blocks, substantially planar products (such as pavers) andhollow products (such as hollow pipes), are formed in a mold whilecarbon dioxide is injected into the concrete in the mold, throughperforations.

All of the above documents that describe reactions of carbon dioxidewith concrete are dealing with concrete that has Portland cement as abinding agent. Portland cement cures in the absence of CO₂ via ahydration reaction.

Furthermore, existing methods typically involve large energy consumptionand carbon dioxide emission with unfavorable carbon footprint.

There is an on-going need for an apparatus and methods for fabricatingnovel composite materials that exhibit useful aesthetic and physicalcharacteristics and can be mass-produced at low cost with improvedenergy consumption and desirable carbon footprint.

SUMMARY OF THE INVENTION

The invention is based in part on the unexpected discovery of novelcomposite materials such as concrete and stone-like materials that canbe readily produced from widely available, low cost precursor materialsin particle form by a process suitable for large-scale production. Theprecursor materials include bonding elements that comprise particulatecalcium silicate (e.g., ground Wollastonite), and particulate fillermaterials that include minerals (e.g., quartz and other SiO₂-containingmaterials, granite, mica and feldspar). A fluid component is alsoprovided as a reaction medium, comprising liquid water and/or watervapor and a reactant, carbon dioxide (CO₂). Additive materials caninclude natural or recycled materials, and calcium carbonate-rich andmagnesium carbonate-rich materials, as well as additives to the fluidcomponent, such as a water-soluble dispersant.

Various additives can be used to fine-tune the physical appearance andmechanical properties of the resulting composite material, such asparticles of colored materials, such as colored glass, colored sand, andcolored quartz particles, and pigments (e.g., black iron oxide, cobaltoxide and chromium oxide). One can use the term “colorants” to refergenerally to either or both of colored materials and pigments. In orderto simulate a slate-like appearance, the particulate filler materialscan include coarse particles and fine particles. The coarse particlesare principally Silicate based materials in order to provide hardness,and the fine particles can be a wide variety of materials, includingsand, ground, crushed or otherwise comminuted substances selected fromminerals and additive materials.

These composite materials may exhibit aesthetic visual patterns as wellas display compressive strength, flexural strength and water absorptionsimilar to that of the corresponding natural materials. The compositematerials of the invention can be produced using the efficientgas-assisted hydrothermal liquid phase sintering (HLPS) process at lowcost and with much improved energy consumption and carbon footprint. Infact, in preferred embodiments of the invention, CO₂ is consumed as areactive species resulting in net sequestration of CO₂.

According to one aspect, the invention features a curing system forcuring a material which requires CO₂ as a curing reagent. The materialdoes not cure in the absence of CO₂. The material does not consume wateras a reagent. The curing system comprises a curing chamber configured tocontain a material that consumes CO₂ as a reactant (or reagent) and thatdoes not cure in the absence of CO₂. The curing chamber having at leastone port configured to allow the material to be introduced into thecuring chamber and to be removed from the curing chamber, and having atleast one closure for the port, the closure configured to provide anatmospheric seal when closed so as to prevent contamination of a gaspresent in the curing chamber by gas outside the curing chamber; asource of carbon dioxide configured to provide gaseous carbon dioxide tothe curing chamber by way of a gas entry port in the curing chamber, thesource of carbon dioxide having at least one flow regulation deviceconfigured to control a flow rate of the gaseous carbon dioxide into thecuring chamber; a gas flow subsystem configured to circulate the gasthrough the curing chamber during a time period when the material thatconsumes CO₂ as a reactant is being cured; a temperature controlsubsystem configured to control a temperature of the gas within thechamber; a humidity control subsystem configured to control a humidityin the gas within the chamber to increase or decrease humidity; and atleast one controller in communication with at least one of the source ofcarbon dioxide, the gas flow subsystem, the temperature controlsubsystem, and the humidity control subsystem; and at least onecontroller configured to control independently during a time period whenthe material that consumes CO₂ as a reactant is being cured at least arespective one of the flow rate of the gaseous carbon dioxide, thecirculation of the gas through the curing chamber, the temperature ofthe gas, and the humidity in the gas.

In one embodiment, the curing chamber is configured to contain apressure of gas therein that is above atmospheric pressure.

In another embodiment, the at least one flow regulation device comprisesat least one of a pressure regulator and a flow controller configured tosupply carbon dioxide gas at a rate substantially equal to a rate ofconsumption of the carbon dioxide by the material that consumes CO₂ as areactant during curing.

In yet another embodiment, the at least one flow regulation devicecomprises at least one of a pressure regulator and a flow controllerconfigured to supply carbon dioxide gas at a rate sufficient to purgeambient atmosphere from the curing chamber in a time period between2-120 minutes to achieve a target CO₂ concentration in a range of 50-90%by volume.

In still another embodiment, the at least one flow regulation devicecomprises at least one of a pressure regulator and a flow controllerconfigured to supply carbon dioxide gas at a rate substantially equal toa rate of venting of the gas from the curing chamber.

In a further embodiment, the gas flow subsystem includes a measurementapparatus configured to measure an amount of carbon dioxide in the gaspresent in the curing chamber.

In one embodiment, the gas flow subsystem includes a measurementapparatus configured to measure a gas velocity of the gas present in thecuring chamber.

In one embodiment, the measurement apparatus configured to measure a gasvelocity is a selected one of a pitot tube, an orifice plate, ananemometer and a laser Doppler detection system.

In one embodiment, the gas flow subsystem includes a variable speedblower configured to circulate gas at a desired velocity in the curingchamber.

In yet a further embodiment, the temperature control subsystem includesa temperature sensor configured to measure the temperature of the gas inthe curing chamber.

In an additional embodiment, the temperature control subsystem includesa heat exchanger to regulate the temperature of the gas in the curingchamber.

In one more embodiment, the temperature control subsystem includes aheat exchanger to control a temperature of the gaseous carbon dioxideprovided to the curing chamber by way of the gas entry port in thecuring chamber.

In still a further embodiment, the temperature control subsystemincludes a heater situated on an external surface of the curing chamberor built into the walls of the chamber.

In one embodiment, the humidity control subsystem includes a measurementapparatus configured to determine a relative humidity of the gas withinthe chamber.

In another embodiment, the humidity control subsystem includes acondenser and one-way water drain of condensate configured to reduce thehumidity in the gas within the chamber.

In yet another embodiment, the humidity control subsystem includes anexhaust valve configured to reduce the humidity in the gas within thechamber.

In still another embodiment, the humidity control subsystem includes awater supply configured to increase the humidity in the gas within thechamber.

In a further embodiment, the at least one controller is a programmablelogic controller.

In yet a further embodiment, the at least one controller is a generalpurpose programmable computer that operates under the control of a setof instructions recorded on a machine-readable medium.

In an additional embodiment, the at least one controller includes adisplay configured to display to a user any of a duration of a curingcycle, the flow rate of the gaseous carbon dioxide, a concentration ofcarbon dioxide in the curing chamber, a pressure of the gas in thecuring chamber, a rate of circulation of the gas through the curingchamber, the temperature of the gas, and the humidity in the gas.

In one more embodiment, the at least one controller is configured torecord any of a duration of a curing cycle, the flow rate of the gaseouscarbon dioxide, a concentration of carbon dioxide in the curing chamber,a pressure of the gas in the curing chamber, a rate of circulation ofthe gas through the curing chamber, the temperature of the gas, and thehumidity in the gas.

In still a further embodiment, the at least one controller includes atouch screen display.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a traditional (prior art) concretecuring chamber.

FIG. 2 is a graph that illustrates a traditional (prior art) concretecuring profile showing temperature as a function of time.

FIGS. 3( a)-3(c) are schematic illustrations of cross-sections ofbonding elements according to exemplary embodiments of the presentinvention, including three exemplary core morphologies: (a) fibrous, (b)elliptical, and (c) equiaxed.

FIGS. 4( a)-4(f) are schematic illustrations of side view and crosssection views of composite materials according to exemplary embodimentsof the present invention, illustrating (a) 1D oriented fiber-shapedbonding elements in a dilute bonding matrix (bonding elements are nottouching), (b) 2D oriented platelet shaped bonding elements in a dilutebonding matrix (bonding elements are not touching), (c) 3D orientedplatelet shaped bonding elements in a dilute bonding matrix (bondingelements are not touching), and (d) randomly oriented platelet shapedbonding elements in a dilute bonding matrix (bonding elements are nottouching), wherein the composite materials includes the bonding matrixand filler components such as polymers, metals, inorganic particles,aggregates etc., (e) a concentrated bonding matrix (with a volumefraction sufficient to establish a percolation network) of bondingelements where the matrix is 3D oriented, and (f) a concentrated bondingmatrix (with a volume fraction sufficient to establish a percolationnetwork) of randomly oriented bonding elements, wherein fillercomponents such as polymers, metals, inorganic particles, aggregatesetc. may be included.

FIG. 5 is a schematic diagram of a CO₂ concrete curing chamberconstructed and operated according to principles of the invention.

FIG. 6 is a schematic diagram of a CO₂ concrete curing chamber thatprovides humidification according to principles of the invention.

FIG. 7 is a schematic diagram of a CO₂ curing chamber that providesdehumidifcation by purging humid gas according to principles of theinvention.

FIG. 8 is a schematic diagram of a CO₂ curing chamber that providesdehumidifcation using a chilled heat exchanger according to principlesof the invention.

FIG. 9 is a schematic diagram of a curing chamber that has a CO₂ purgeline and a constant flow CO₂ replenishment line according to principlesof the invention.

FIG. 10 is a schematic diagram of a curing chamber that has a CO₂ purgeline and that can provide regulated pressure CO₂ replenishment accordingto principles of the invention.

FIG. 11 is a schematic diagram of a midsized curing chamber withmultiple methods of humidity control as well as ability to control andreplenish CO₂ using constant flow or pressure regulation and that cancontrol humidity according to principles of the invention.

FIG. 12 is an image of several drum reactors constructed from 55 gallonstainless steel drums.

FIG. 13 is an image of the interior of a drum reactor including racks tosupport pallets of materials to be processed therein.

FIG. 14 is an image of the exterior of a drum reactor surrounded by aheating jacket, and showing several thermocouple connectors and a gasentry port.

FIG. 15 is an image of a control panel for a drum reactor showing fourcontrollers that control (from left to right) an immersion heater, ajacket heater, an inline gas heater, and a fan, with readouts for thetemperatures of the three heaters.

FIG. 16 is an image of a commercially available concrete curing chamberbuilt by CDS Inc. which has been retrofitted for low pressure CO₂ curingaccording to principles of the invention.

FIG. 17 is an image of a portion of the interior of the chamber of FIG.16, showing further modifications made to the prior art Portland cementcuring system.

FIG. 18 is another view of the CO₂ NDIR analyzer 1740.

FIG. 19 is a view within the curing chamber that illustrates additionalcomponents that have been added.

FIG. 20 is a screen shot of the display connected to a programmablelogic controller that controls a curing chamber according to principlesof the invention.

FIG. 21 is the corresponding temperature and humidity profile for theexample 5.

FIG. 22 is the corresponding temperature and humidity profile for theexample 6.

DETAILED DESCRIPTION OF THE INVENTION

The essence of this invention is a curing system that creates acontrolled atmosphere whereby temperature, pressure, CO₂ concentration,relative humidity and gas velocity are monitored and controlled tocreate final concrete-based products that will predominately cure in thepresence of CO₂ and will not fully cure in the absence of CO₂.

Composite Materials Made by Hydrothermal Liquid Phase Sintering

This invention provides apparatus and methods used to manufacture novelcomposite materials that are cured predominantly by a CO₂ consumptionreaction, that exhibit useful properties and can be readily producedfrom widely available, low cost precursor materials by a processsuitable for large-scale production with minimal environmental impact.The precursor materials include inexpensive and abundant calciumsilicate and calcium carbonate rich materials, for example, groundWollastonite, ground limestone, coarse particles and fine particles. Thecoarse particles and the fine particles are principally SiO₂ basedmaterials in order to provide hardness. The coarse and fine particlescan include minerals (e.g., quartz and other SiO₂-bearing materials,granite, mica and feldspar). Other key process components include waterand CO₂. Various additives can be used to modify and fine-tune thephysical appearance and/or mechanical properties of the resultingcomposite material, such as using pigments (e.g., black iron oxide,cobalt oxide and chromium oxide) and colored glass and/or coloredquartz.

These composite materials display various patterns, textures and othercharacteristics, such as visual patterns of various colors. In addition,the composite materials of the invention exhibit compressive strength,flexural strength and water absorption properties similar toconventional concrete or the corresponding natural materials.Furthermore, the composite materials can be produced, as disclosedherein, using the energy-efficient HLPS process and can be manufacturedat low cost and with favorable environmental impact. For example inpreferred embodiments of the invention, CO₂ is used as a reactivespecies resulting in sequestration of CO₂ in the produced compositematerials with in a carbon footprint unmatched by any existingproduction technology. The HLPS process is thermodynamically driven bythe free energy of the chemical reaction(s) and reduction of surfaceenergy (area) caused by crystal growth. The kinetics of the HLPS processproceed at a reasonable rate at low temperature because a solution(aqueous or nonaqueous) is used to transport reactive species instead ofusing a high melting point fluid or high temperature solid-state medium.

Discussions on various aspects of HLPS can be found in U.S. Pat. No.8,114,367, U.S. Pub. No. US 2009/0143211 (application Ser. No.12/271,566), U.S. Pub. No. US 2011/0104469 (application Ser. No.12/984,299), U.S. Pub. No. 20090142578 (application Ser. No.12/271,513), WO 2009/102360 (PCT/US2008/083606), WO 2011/053598(PCT/US2010/054146), WO 2011/090967 (PCT/US2011/021623), U.S.application Ser. No. 13/411,218 filed Mar. 2, 2012 (Riman et al.), U.S.application Ser. No. 13/491,098 filed Jun. 7, 2012 (Riman et al), U.S.Provisional Patent Application No. 61/708,423 filed Oct. 1, 2012, andU.S. Provisional Patent Application Nos. 61/709,435, 61/709,453,61/709,461, and 61/709,476, all filed Oct. 4, 2012, each of which isexpressly incorporated herein by reference in its entirety for allpurposes.

In certain embodiments, the composite further includes a pigment. Thepigment may be evenly dispersed or substantially unevenly dispersed inthe bonding matrices, depending on the desired composite material. Thepigment may be any suitable pigment including, for example, oxides ofvarious metals (e.g., iron oxide, cobalt oxide, chromium oxide) Thepigment may be of any color or colors, for example, selected from black,white, blue, gray, pink, green, red, yellow and brown. The pigment maybe present in any suitable amount depending on the desired compositematerial, for example in an amount ranging from about 0.0% to about 10%by weight (e.g., about 0.0% to about 8%, about 0.0% to about 6%, about0.0% to about 5%, about 0.0% to about 4%, about 0.0% to about 3%, about0.0% to about 2%, about 0.0% to about 1%, about 0.0% to about 0.5%,about 0.0% to about 0.3%, about 0.0% to about 2%, about 0.0% to about0.1%).

The plurality of bonding elements may have any suitable median particlesize and size distribution dependent on the desired composite material.In certain embodiments, the plurality of bonding elements have a medianparticle size in the range of about 5 μm to about 100 μm (e.g., about 5μm to about 80 μm, about 5 μm to about 60 μm, about 5 μm to about 50 μm,about 5 μm to about 40 μm, about 5 μm to about 30 μm, about 5 μm toabout 20 μm, about 5 μm to about 10 μm, about 10 μm to about 80 μm,about 10 μm to about 70 μm, about 10 μm to about 60 μm, about 10 μm toabout 50 μm, about 10 μm to about 40 μm, about 10 μm to about 30 μm,about 10 μm to about 20 μm).

The plurality of filler particles may have any suitable median particlesize and size distribution. In certain embodiments, the plurality offiller particles has a median particle size in the range from about 5 μmto about 7 mm (e.g., about 5 μm to about 5 mm, about 5 μm to about 4 mm,about 5 μm to about 3 mm, about 5 μm to about 2 mm, about 5 μm to about1 mm, about 5 μm to about 500 μm, about 5 μm to about 300 μm, about 20μm to about 5 mm, about 20 μm to about 4 mm, about 20 μm to about 3 mm,about 20 μm to about 2 mm, about 20 μm to about 1 mm, about 20 μm toabout 500 μm, about 20 μm to about 300 μm, about 100 μm to about 5 mm,about 100 μm to about 4 mm, about 100 μm to about 3 mm, about 100 μm toabout 2 mm, about 100 μm to about 1 mm).

In certain preferred embodiments, the filler particles are made from acalcium carbonate-rich material such as limestone (e.g., groundlimestone). In certain materials, the filler particles are made from oneor more of SiO2-based or silicate-based material such as quartz, mica,granite, and feldspar (e.g., ground quartz, ground mica, ground granite,ground feldspar).

In certain embodiments, filler particles may include natural, syntheticand recycled materials such as glass, recycled glass, coal slag, calciumcarbonate-rich material and magnesium carbonate-rich material.

The plurality of bonding elements may be chemically transformed from anysuitable precursor materials, for example, from a precursor calciumsilicate other than wollastonite. The precursor calcium silicate mayinclude one or more chemical elements of aluminum, magnesium and iron.

As used herein, the term “calcium silicate” refers tonaturally-occurring minerals or synthetic materials that are comprisedof one or more of a group of calcium-silicon-containing compoundsincluding CaSiO₃ (also known as “Wollastonite” or “pseudo-wollastonite”and sometimes formulated as CaO.SiO₂), Ca₃Si₂O₇ (also known as“Rankinite” and sometimes formulated as 3CaO.2SiO₂), Ca₂SiO₄ (also knownas “Belite” and sometimes formulated as 2CaO.SiO₂), Ca₃SiO₅ (also knownas “Alite” and sometimes formulated as 3CaO.SiO₂), which material mayinclude one or more other metal ions and oxides (e.g., aluminum,magnesium, iron or manganese oxides), or blends thereof, or may includean amount of magnesium silicate in naturally-occurring or syntheticform(s) ranging from trace amount (1%) to about 50% or more by weight.

It should be understood that, compositions and methods disclosed hereincan be adopted to use magnesium silicate in place of or in addition tocalcium silicate. As used herein, the term “magnesium silicate” refersto nationally-occurring minerals or synthetic materials that arecomprised of one or more of a groups of magnesium-silicon-containingcompounds including, for example, Mg₂SiO₄ (also known as “Fosterite”)and Mg₃Si₄O₁₀(OH)₂) (also known as “Talc”), which material may includeone or more other metal ions and oxides (e.g., calcium, aluminum, ironor manganese oxides), or blends thereof, or may include an amount ofcalcium silicate in naturally-occurring or synthetic form(s) rangingfrom trace amount (1%) to about 50% or more by weight.

The term “quartz”, as used herein, refers to any SiO₂-based material,including common sands (construction and masonry), as well as glass andrecycled glass. The term also includes any other recycled natural andsynthetic materials that contain significant amounts of SiO₂ (e.g., micasometimes formulated as KAl₂(AlSi₃O₁₀)).

The weight ratio of (bonding elements):(filler particles) may be anysuitable rations dependent on the desired composite material, forexample, in the range of about (15 to 50):about (50 to 85).

In certain preferred embodiments, the plurality of bonding elements areprepared by chemical transformation from ground wollastonite (or anon-wollastonite precursor calcium silicate or magnesium silicate) byreacting it with CO₂ via a gas-assisted HLPS process.

In certain embodiments, the composite material is characterized by acompressive strength from about 90 MPa to about 175 MPa (e.g., about 90MPa to about 150 MPa, about 90 MPa to about 140 MPa, about 90 MPa toabout 130 MPa, about 90 MPa to about 120 MPa, about 90 MPa to about 110MPa, about 100 MPa to about 175 MPa, about 120 MPa to about 175 MPa,about 130 MPa to about 175 MPa, about 140 MPa to about 175 MPa, about150 MPa to about 175 MPa, about 160 MPa to about 175 MPa).

In certain embodiments, the composite material is characterized by aflexural strength from about 5 MPa to about 30 MPa (e.g., about 5 MPa toabout 25 MPa, about 5 MPa to about 20 MPa, about 5 MPa to about 15 MPa,about 5 MPa to about 10 MPa, about 10 MPa to about 30 MPa, about 20 MPato about 30 MPa, about 25 MPa to about 30 MPa).

In certain embodiments, the composite material is characterized by waterabsorption of less than about 10% (e.g., less than about 8%, 5%, 4%, 3%,2%, 1%).

In certain embodiments, the composite material has less than about 10%by weight of one or more minerals selected from quartz, mica, feldspar,calcium carbonate and magnesium carbonate.

The composite material may display any desired textures, patterns andphysical properties, in particular those that are characteristic ofnatural stone. In certain preferred embodiments, the composite materialexhibits a visual pattern similar to natural stone. Othercharacteristics include colors (e.g., black, white, blue, pink, grey(pale to dark), green, red, yellow, brown, cyan (bluish-green) orpurple) and textures.

In another aspect, the invention generally relates to a process forpreparing a composite material. The process includes: mixing aparticulate composition and a liquid composition to create a slurrymixture; forming the slurry mixture into a desired shape, either bycasting the slurry into a mold, pressing the slurry in a mold, pressingthe slurry in a vibrating mold, extruding the slurry, slip forming theslurry, or using any other shape-forming method common in concreteproduction; and curing the formed slurry mixture at a temperature in therange from about 20° C. to about 150° C. for about 1 hour to about 80hours under a vapor comprising water and CO₂ and having a pressure inthe range from about ambient atmospheric pressure to about 50 psi aboveambient atmospheric pressure and having a CO₂ concentration ranging fromabout 10% to about 90% to produce a composite material exhibiting atexture and/or a pattern.

The particulate composition includes a ground calcium silicate having amedian particle size in the range from about 1 μm to about 100 μm, and aground calcium carbonate or a SiO₂ bearing material having a medianparticle size in the range from about 3 μm to about 7 mm. The liquidcomposition includes water and a water-soluble dispersant.

In certain embodiments, the particulate composition further includes asecond ground calcium carbonate having substantially smaller or largermedian particle size than the first ground limestone. The process canfurther include, before curing the casted mixture, the step of dryingthe casted mixture. The particulate composition further comprises apigment or a colorant as discussed herein.

In certain embodiments, curing the formed slurry mixture is performed ata temperature in the range from about 30° C. to about 120° C. for about1 hours to about 70 hours under a vapor comprising water and CO₂ andhaving a pressure in the range from about ambient atmospheric pressureto about 30 psi above ambient atmospheric pressure.

In certain embodiments, curing the formed slurry mixture is performed ata temperature in the range from about 60° C. to about 110° C. for about1 hours to about 70 hours under a vapor comprising water and CO₂ andhaving a pressure in the range from about ambient atmospheric pressureto about 30 psi above ambient atmospheric pressure.

In certain embodiments, curing the formed slurry mixture is performed ata temperature in the range from about 80° C. to about 100° C. for about1 hours to about 60 hours under a vapor comprising water and CO₂ andhaving a pressure in the range from about ambient atmospheric pressureto about 30 psi above ambient atmospheric pressure.

In certain embodiments, curing the formed slurry mixture is performed ata temperature equal to or lower than about 60° C. for about 1 to about50 hours under a vapor comprising water and CO₂ and having an ambientatmospheric pressure.

In certain embodiments, the ground calcium silicate includes primarilyground Wollastonite, the first ground calcium carbonate includesprimarily a first ground limestone, and the second ground calciumcarbonate includes primarily a second ground limestone.

For example, in some embodiments, the ground Wollastonite has a medianparticle size from about 5 μm to about 50 μm (e.g., about 5 μm, 10 μm,15 μm, 20 μm, 25 μm, 30 μm, 40 μm, 90 μm), a bulk density from about 0.6g/mL to about 0.8 g/mL (loose) and about 1.0 g/mL to about 1.2 g/mL(tapped), a surface area from about 1.5 m²/g to about 2.0 m²/g. Thefirst ground SiO₂ bearing material has a median particle size from about40 μm to about 90 μm (e.g., about 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 30μm, 90 μm), a bulk density from about 0.7 g/mL to about 0.9 g/mL (loose)and about 1.3 g/mL to about 1.6 g/mL (tapped).

In certain preferred embodiments, the liquid composition includes waterand a water-soluble dispersant comprising a polymer salt (e.g., anacrylic homopolymer salt) having a concentration from about 0.1% toabout 2% w/w of the liquid composition.

In yet another aspect, the invention generally relates to a compositematerial prepared according to a process disclosed herein, for example,a composite material having a compressive strength from about 90 MPa toabout 175 MPa and a flexural strength from about 5.4 MPa to about 20.6MPa.

In yet another aspect, the invention generally relates to an article ofmanufacture made from a composite material disclosed herein.

Any suitable precursor materials may be employed. For example calciumsilicate particles formed primarily of Wollastonite, CaSiO₃, can reactwith carbon dioxide dissolved in water. It is believed that calciumcations are leached from the Wollastonite and transform the peripheralportion of the Wollastonite core into calcium-deficient Wollastonite. Asthe calcium cations continue to be leached from the peripheral portionof the core, the structure of the peripheral portion eventually becomeunstable and breaks down, thereby transforming the calcium-deficientWollastonite peripheral portion of the core into a predominantlysilica-rich first layer. Meanwhile, a predominantly calcium carbonatesecond layer precipitates from the water.

More specifically, the first layer and second layer may be formed fromthe precursor particle according the following reaction (1):CaSiO₃(s)+CO₂(g)=CaCO₃(s)+SiO₂(s) ΔH°=−87 kJ/mol CO₂  (1)For example, in a silicate mineral carbonation reaction such as withWollastonite, CO₂ is introduced as a gas phase that dissolves into aninfiltration fluid, such as water. The dissolution of CO₂ forms acidiccarbonic species that results in a decrease of pH in solution. Theweakly acidic solution incongruently dissolves calcium species fromCaSiO₃. The released calcium cations and the dissociated carbonatespecies lead to the precipitation of insoluble carbonates. Silica-richlayers are thought to remain on the mineral particles as calciumdepleted layers.

Thus, according to a preferred embodiment of the invention, CO₂preferentially reacts with the calcium cations of the Wollastoniteprecursor core, thereby transforming the peripheral portion of theprecursor core into a silica-rich first layer and a calciumcarbonate-rich second layer. Also, the presence of the first and secondlayers on the core act as a barrier to further reaction betweenWollastonite and carbon dioxide, resulting in the bonding element havingthe core, first layer and second layer.

In some embodiments, silicate materials having metals other than Ca orin addition to Ca, for example Fosterite (Mg₂SiO₄), Diopside(CaMgSi₂O₆), and Talc (Mg₃Si₄O₁₀(OH)₂) can react with carbon dioxidedissolved in water in a manner similar to the reaction of Wollastonite,as described above. It is believed that such silicate materials can beused, alone, in combination, and/or in combination with Wollastonite, asprecursors for bonding elements according to principles of theinvention.

Preferably, gas-assisted HLPS processes utilize partially infiltratedpore space so as to enable gaseous diffusion to rapidly infiltrate theporous preform and saturate thin liquid interfacial solvent films in thepores with dissolved CO₂. CO₂-based species have low solubility in purewater (1.5 g/L at 25° C., 1 atm.). Thus, a substantial quantity of CO₂must be continuously supplied to and distributed throughout the porouspreform to enable significant carbonate conversion. Utilizing gas phasediffusion offers a huge (about 100-fold) increase in diffusion lengthover that of diffusing soluble CO₂ an equivalent time in a liquid phase.(“Handbook of chemistry and physics”, Editor: D. R. Lide, Chapters 6 and8, 87^(th) Edition 2006-2007, CRC.) This partially infiltrated stateenables the reaction to proceed to a high degree of carbonation in afixed period of time.

Liquid water in the pores speeds up the reaction rate because it isessential for ionization of both carbonic acid and calcium species.However, water levels need to be low enough such that CO₂ gas candiffuse into the porous matrix prior to dissolution in the pore-boundwater phase. Furthermore, the actively dissolving porous preform servesas a template for expansive reactive crystal growth. Thus, the bondingelement and matrices can be formed with minimal distortion and residualstresses. This enables large and complex shapes to result, such as thoseneeded for infrastructure and building materials, in addition to manyother applications.

Thus, various combinations of curing conditions may be devised toachieve the desired production process, including varied reactiontemperatures, pressures and lengths of reaction. In a first exemplaryembodiment, water is delivered to the precursor materials in liquid formwith CO₂ dissolved therein and the curing process is conducted at about90° C. and about 20 psig (i.e., 20 psi above ambient pressure) for about48 hours. In a second exemplary embodiment, water is present in theprecursor material (e.g., as residual water from prior mixing step) andwater vapor is provided to precursor materials (e.g., to maintain waterlevel and/or prevent loss of water from evaporating) along with CO₂ andthe curing process is performed at about 60° C. and 0 psig (at ambientatmospheric pressure) for about 19 hours. In a third exemplaryembodiment, water is delivered to precursor materials in vapor formalong with CO₂ and the curing process is performed at about 90° C. and20 psig (20 psi above ambient atmospheric pressure) for about 19 hours.

In yet another aspect, the invention generally relates to a compositematerial that includes: a plurality of bonding elements and a pluralityof filler particles. Each bonding element includes: a core comprisingprimarily magnesium silicate, a silica-rich first or inner layer, and amagnesium carbonate-rich second or outer layer. The plurality of bondingelements and the plurality of filler particles together form one or morebonding matrices and the bonding elements and the filler particles aresubstantially evenly dispersed therein and bonded together, whereby thecomposite material exhibits one or more textures, patterns and physicalproperties.

Compositions and methods disclosed herein in connection with calciumsilicate can be adopted to use magnesium silicate in place of or inaddition to calcium silicate.

B. Bonding Elements, Bonding Matrices and Composite Materials

B1. Bonding Elements

As schematically illustrated in FIGS. 3( a)-3(c), a bonding elementincludes a core (represented by the black inner portion), a first layer(represented by the white middle portion) and a second or encapsulatinglayer (represented by the outer portion). The first layer may includeonly one layer or multiple sub-layers and may completely or partiallycover the core. The first layer may exist in a crystalline phase, anamorphous phase or a mixture thereof, and may be in a continuous phaseor as discrete particles. The second layer may include only one layer ormultiple sub-layers and may also completely or partially cover the firstlayer. The second layer may include a plurality of particles or may beof a continuous phase, with minimal discrete particles.

A bonding element may exhibit any size and any regular or irregular,solid or hollow morphology depending on the intended application.Exemplary morphologies include: cubes, cuboids, prisms, discs, pyramids,polyhedrons or multifaceted particles, cylinders, spheres, cones, rings,tubes, crescents, needles, fibers, filaments, flakes, spheres,sub-spheres, beads, grapes, granulars, oblongs, rods, ripples, etc.

In general, as discussed in greater detail herein, a bonding element isproduced from reactive precursor materials (e.g., precursor particles)through a transformation process. The precursor particles may have anysize and shape as long as they meet the needs of the intendedapplication. The transformation process generally leads to thecorresponding bonding elements having similar sizes and shapes of theprecursor particles.

Precursor particles can be selected from any suitable material that canundergo suitable transformation to form the desired bonding elements.For example, the precursor particles may include oxides and non-oxidesof silicon, titanium, aluminum, phosphorus, vanadium, tungsten,molybdenum, gallium, manganese, zirconium, germanium, copper, niobium,cobalt, lead, iron, indium, arsenic, tantalum, and/or alkaline earthelements (beryllium, magnesium, calcium, strontium, barium and radium).

Exemplary precursor materials include oxides such as silicates,titanates, aluminates, phosphates, vanadates, tungstates, molybdates,gallates, manganates, zirconates, germinates, cuprates, stannates,hafnates, chromates, niobates, cobaltates, plumbates, ferrites, indates,arsenates, tantalates and combinations thereof. In some embodiments, theprecursor particles include silicates such as orthosilicates,sorosilicates, cyclosilicates, inosilicates, phyllosilicates,tectosilicates and/or calcium silicate hydrate.

Certain waste materials may be used as the precursor particles for someapplications. Waste materials may include, for example, minerals,industrial waste, or an industrial chemical material. Some exemplarywaste materials include mineral silicate, iron ore, periclase, gypsum,iron (II) hydroxide, fly ash, bottom ash, slag, glass, oil shells, redmud, battery waste, recycled concrete, mine tailings, paper ash, orsalts from concentrated reverse osmosis brine.

Additional precursor particles may include different types of rockcontaining minerals such as cal-silicate rock, fitch formation, hebrongneiss, layered gneiss, middle member, argillite, quartzite,intermediate Precambrian sediments, dark-colored, feldpathic quartzitewith minor limestone beds, high-grade metasedimentry biotite schist,biotite gniss, mica schist, quartzite, hoosac formation, partridgeformation, Washington gneiss, Devonian, Silurian greenvale coveformation, ocoee supergroup, metasandstone, metagraywacke, Rangeleyformation, amphibolites, calcitic and dolomite marble, manhattanformation, rusty and gray biotite-quartz-feldspar gneiss, and waterfordgroup.

Precursor particles may also include igneous rocks such as, andesite,anorthosite, basinite, boninite, carbonatite and charnockite,sedimentary materials such as, but not limited to, argillite, arkose,breccias, cataclasite, chalk, claystone, chert, flint, gitsone, lighine,limestone, mudstone, sandstone, shale, and siltsone, metamorphicmaterials such as, but not limited to, amphibolites, epidiorite, gneiss,granulite, greenstone, hornfels, marble, pelite, phyllite, quartzite,shist, skarn, slate, talc carbonate, and soapstone, and other varietiesof rocks such as, but not limited to, adamellite, appinite, aphanites,borolanite, blue granite, epidosite, felsites, flint, ganister, ijolite,jadeitite, jasproid, kenyte, vogesite, larvikite, litchfieldite,luxullianite, mangerite, minette, novaculite, pyrolite, rapakivigranite, rhomb porphyry, shonkinite, taconite, teschenite, theralite,and variolite.

Table 1 provides exemplary embodiments of different types of chemistriesfor the first and second layers that can be achieved when usingdifferent precursor materials. Regarding the first layer, by usingdifferent precursor materials one may obtain silica, alumina or titania.The second layer may also be modified with the selection of theprecursor material. For example, the second layer may include varioustypes of carbonates such as, pure carbonates, multiple cationscarbonates, carbonates with water or an OH group, layered carbonateswith either water or an OH group, anion containing carbonates, silicatecontaining carbonates, and carbonate-bearing minerals.

TABLE 1 Exemplary Precursors and Encapsulating layers Raw Material(Precursor) First Layer Encapsulating Layer Wollastonite (CaSiO₃)Silica-rich CaCO₃ Fosterite (Mg₂SiO₄) MgCO₃ Diopside (CaMgSi₂O₆)(Ca,Mg)CO₃ Talc (Mg₃Si₄O₁₀(OH)₂) MgCO₃ xH₂O (x = 1-5) GlaucophaneAlumina MgCO₃ and/or (Na₂Mg₃Al₂Si₈O₂₂(OH)₂) and/or NaAlCO₃(OH)₂Palygorskite Silica- Mg₆Al₂CO₃(OH)₁₆4H₂O ((Mg,Al)₂Si₄O₁₀(OH)•4(H₂O))rich Meionite Ca₂SO₄CO₃.4H₂O (Ca₄(Al₂Si₂O8)₃(Cl₂CO₃,SO₄)) TanzaniteCa₅Si₂O₈CO₃ and/or (Ca₂Al₃O(SiO₄)(Si₂O₇)(OH)) Ca₅Si₂O₈CO₃ and/orCa₇Si₆O₁₈CO₃.2H₂O (Ba_(0.6)Sr_(0.3)Ca_(0.1))TiO₃ Titania- richSr(Sr,Ca,Ba)(CO₃)₂

The second layer may be modified by introducing additional anions and/orcations. Such additional anions and cations may be used to modify thesecond layer to increase its physical and chemical properties such asfire resistance or acid resistance. For example, as shown in Table 2,while the first layer is retained as a silica-rich layer, the secondlayer may be modified by adding extra anions or cations to the reaction,such as PO₄ ²⁻ and SO₄ ²⁻. As a result, the second layer may include,for example, different phosphate, sulphate, fluoride or combinationsthereof

TABLE 2 Examples of Cation/Anion Sources (in addition to CO₃ ²⁻) CoreFirst Extra anion/cation Particle Laver source Encapsulating LayerCarbonate Type CaSiO₃ Silica- Phosphates Ca₅(PO₄,CO₃)₃OH Phosphatebearing carbonates rich layer Sulphates Ca₂SO₄CO₃•4H₂O Sulphate bearingcarbonates Fluorides Ca₂CO₃F₂ Fluorides bearing carbonates Phosphatesand Ca₅(PO₄,CO₃)₃F Fluoride and phosphates bearing fluorides carbonatesMg⁺² source like CaMg(CO₃)₂ Multiple cation carbonates chlorides,nitrates, hydroxides etc. A combination ofCa₆Mg₂(SO₄)₂(CO₃)₂Cl₄(OH)₄•7H₂O Post-1992 Carbonate-Bearing cation andanion Minerals sourcesB2. Bonding Matrix and Composite Material

A bonding matrix comprises a plurality of bonding elements, forming athree-dimensional network. The bonding matrix may be porous ornon-porous. The degree of porosity depends on a number of variables thatcan be used to control porosity, such as temperature, reactor design,the precursor material and the amount of liquid that is introducedduring the transformation process. Depending on the intendedapplication, the porosity can be set to almost any degree of porosityfrom about 1 vol. % to about 99 vol. %.

The bonding matrix may incorporate one or more filler materials, whichare mixed with the precursor materials prior to or during thetransformation process to create the composite material. Theconcentration of bonding elements in the bonding matrix may vary. Forexample, the concentration of bonding elements on a volume basis may berelatively high, wherein at least some of the bonding elements are incontact with one another. This situation may arise if filler material isincorporated into the bonding matrix, but the type of filler materialand/or the amount of filler material is such that the level ofvolumetric dilution of the bonding element is relatively low. In anotherexample, the concentration of bonding elements on a volume basis may berelatively low, wherein the bonding elements are more widely dispersedwithin the bonding matrix such that few, if any of the bonding elementsare in contact with one another. This situation may arise if fillermaterial is incorporated into the bonding matrix, and the type of fillermaterial and/or the amount of filler material is such that the level ofdilution is relatively high.

In general, the filler material may include any one of a number of typesof materials that can be incorporated into the bonding matrix. A fillermaterial may be inert or active. An inert material does not go throughany chemical reaction during the transformation and does not act as anucleation site, although it may physically or mechanically interactwith the bonding matrix. The inert material may involve polymers,metals, inorganic particles, aggregates, and the like. Specific examplesmay include, but are not limited to basalt, granite, recycled PVC,rubber, metal particles, alumina particle, zirconia particles,carbon-particles, carpet particles, Kevlar™ particles and combinationsthereof. An active material chemically reacts with the bonding matrixduring the transformation go through any chemical reaction during thetransformation and/or acts as a nucleation site. For example, magnesiumhydroxide may be used as a filler material and may chemically react witha dissolving calcium component phase from the bonding matrix to formmagnesium calcium carbonate.

The bonding matrix may occupy almost any percentage of a compositematerial. Thus, for example, the bonding matrix may occupy about 1 vol.% to about 99 vol. % of the composite material (e.g., the volumefraction of the bonding matrix can be less than or equal to about 90vol. %, 70 vol. %, 50 vol. %, 40 vol. %, 30 vol. %, 20 vol. %, 10 vol.%). A preferred range for the volume fraction of the bonding matrix isabout 8 vol. % to about 90 vol. % (e.g., about 8 vol. % to about 80 vol.%, about 8 vol. % to about 70 vol. %, about 8 vol. % to about 50 vol. %,about 8 vol. % to about 40 vol. %), and more preferred range of about 8vol. % to 30 vol. %.

A composite material may also be porous or non-porous. The degree ofporosity depends on a number of variables that can be used to controlporosity, such as temperature, reactor design, the precursor material,the amount of liquid that is introduced during the transformationprocess and whether any filler is employed. Depending on the intendedapplication, the porosity can be set to almost any degree of porosityfrom about 1 vol. % to about 99 vol. % (e.g., less than or equal toabout 90 vol. %, 70 vol. %, 50 vol. %, 40 vol. %, 30 vol. %, 20 vol. %,10 vol. %). A preferred range of porosity for the composite material isabout 1 vol. % to about 70 vol. %, more preferably between about 1 vol.% and about 10 vol. % for high density and durability and between about50 vol. % and about 70 vol. % for lightweight and low thermalconductivity.

Within the bonding matrix, the bonding elements may be positioned,relative to each other, in any one of a number of orientations. FIGS. 4(a)-4(f) schematically illustrate an exemplary bonding matrix thatincludes fiber- or platelet-shaped bonding elements in differentorientations possibly diluted by the incorporation of filler material,as represented by the spacing between the bonding elements. FIG. 4( a),for example, illustrates a bonding matrix that includes fiber-shapedbonding elements aligned in a one-direction (“1-D”) orientation (e.g.,aligned with respect to the x direction). FIG. 4( b) illustrates abonding matrix that includes platelet-shaped bonding elements aligned ina two-direction (“2-D”) orientation (e.g., aligned with respect to the xand y directions). FIG. 4( c) illustrates a bonding matrix that includesplatelet-shaped bonding elements aligned in a three-direction (“3-D”)orientation (e.g., aligned with respect to the x, y and z directions).FIG. 4( d) illustrates a bonding matrix that includes platelet-shapedbonding elements in a random orientation, wherein the bonding elementsare not aligned with respect to any particular direction. FIG. 4( e)illustrates a bonding matrix that includes a relatively highconcentration of platelet-shaped bonding elements that are aligned in a3-D orientation. FIG. 4( f) illustrates a bonding matrix that includes arelatively low concentration of platelet-shaped bonding elements thatare situated in a random orientation (a percolation network). Thecomposite material of FIG. 4( f) achieves the percolation thresholdbecause a large proportion of the bonding elements are touching oneanother such that a continuous network of contacts are formed from oneend of the material to the other end. The percolation threshold is thecritical concentration above which bonding elements show long-rangeconnectivity with either an ordered, e.g., FIG. 4( e), or randomorientation, e.g., FIG. 4( f), of bonding elements. Examples ofconnectivity patterns can be found in, for example, Newnham, et al.,“Connectivity and piezoelectric-pyroelectric composites”, Mat. Res.Bull. vol. 13, pp. 525-536, 1978).

Furthermore, one or multi-level repeating hierarchic structure can beachieved in a manner that can promote dense packing, which provides formaking a strong material, among other potential useful, functionalpurposes. Hierarchy describes how structures form patterns on severallength scales. Different types of bonding matrices can be created byvarying the matrix porosity and by incorporating core fibers ofdifferent sizes. Different kinds of particulate and fiber components canbe used with hierarchic structures to fabricate different kinds ofstructures with different connectivity.

C. Processes of Forming the Bonding Elements, Bonding Matrices andComposite Materials

The transformation (curing) process proceeds by exposing the precursormaterial to a reactive liquid. A reactant associated with the liquidreacts with the chemical ingredients that make up the precursorparticles, and more specifically, the chemical reactants in theperipheral portion of the precursor particles. This reaction eventuallyresults in the formation of the first and second layers.

In some embodiments, the precursor particles include two or morechemical elements. During the transformation process, the reactant inthe liquid preferentially reacts with at least a first one of thechemical elements, wherein the reaction between the reactant in theliquid (e.g., CO₂ and related species in solution) and the at least onefirst chemical element (e.g., calcium²⁺) results in the formation of thefirst and second layers, the first layer comprising a derivative of theprecursor particle, generally excluding the at least one first chemicalelement, whereas the second layer comprises a combination (e.g., CaCO₃)of the reactant and the at least one first chemical element. Incomparison, the core comprises the same or nearly the same chemicalcomposition as the precursor particle (e.g., CaSiO₃). For example,peripheral portions of the core may vary from the chemical compositionof the precursor particle due to selective leaching of particularchemical elements from the core.

Thus, the core and the second layer share the at least one firstchemical element (e.g., calcium²⁺) of the precursor particle, and thecore and the first layer share at least another one of the chemicalelements of the precursor particle (e.g., Si⁴⁺). The at least one firstchemical element shared by the core and the second layer may be, forexample, at least one alkaline earth element (beryllium, magnesium,calcium, strontium, barium and radium). The at least another one of thechemical elements shared by the core and the first layer may be, forexample, silicon, titanium, aluminum, phosphorus, vanadium, tungsten,molybdenum, gallium, manganese, zirconium, germanium, copper, niobium,cobalt, lead, iron, indium, arsenic and/or tantalum.

In some embodiments, the reaction between the reactant in the liquidphase and the at least one first chemical element of the precursorparticles may be carried out to completion thus resulting in the firstlayer becoming the core of the bonding element and having a chemicalcomposition that is different from that of the precursor particles, andat least one additional or second shell layer comprising a compositionthat may or may not include the at least one first chemical element ofthe two or more chemical elements of the precursor particles.

C1. Gas-Assisted Hydrothermal Liquid Phase Sintering

The bonding elements may be formed, for example, by a method based ongas-assisted HLPS. In such a method, a porous solid body including aplurality of precursor particles is exposed to a liquid (solvent), whichpartially saturates the pores of the porous solid body, meaning that thevolume of the pores are partially filled with water.

In certain systems such as those forming carbonate, completely fillingthe pores with water is believed to be undesirable because the reactivegas is unable to diffuse from the outer surface of the porous solid bodyto all of the internal pores by gaseous diffusion. Instead, the reactantof the reactive gas would dissolve in the liquid and diffuse in theliquid phase from the outer surface to the internal pores, which is muchslower. This liquid-phase diffusion may be suitable for transformingthin porous solid bodies but would be unsuitable for thicker poroussolid bodies.

In some embodiments, a gas containing a reactant is introduced into thepartially saturated pores of the porous solid body and the reactant isdissolved by the solvent. The dissolved reactant then reacts with the atleast first chemical element in the precursor particle to transform theperipheral portion of the precursor particle into the first layer andthe second layer. As a result of the reaction, the dissolved reactant isdepleted from the solvent. Meanwhile, the gas containing the reactantcontinues to be introduced into the partially saturated pores to supplyadditional reactant to the solvent.

As the reaction between the reactant and the at least first chemicalelement of the precursor particles progresses, the peripheral portion ofthe precursor particle is transformed into the first layer and thesecond layer. The presence of the first layer at the periphery of thecore eventually hinders further reaction by separating the reactant andthe at least first chemical element of the precursor particle, therebycausing the reaction to effectively stop, leaving a bonding elementhaving the core as the unreacted center of the precursor particle, thefirst layer at a periphery of the core, and a second layer on the firstlayer.

The resulting bonding element includes the core, the first layer and thesecond layer, and is generally larger in size than the precursorparticle, filling in the surrounding porous regions of the porous solidbody and possibly bonding with adjacent materials in the porous solidbody. As a result, net-shape formation of products may be formed thathave substantially the same size and shape as but a higher density thanthe porous solid body. This is an advantage over traditionally sinteringprocesses that cause shrinkage from mass transport to produce a higherdensity material than the initial powder compact.

C2. HLPS in an Autoclave

In an exemplary embodiment of the method of HLPS, a porous solid bodycomprising a plurality of precursor particles is placed in an autoclavechamber and heated. Water as a solvent is introduced into the pores ofthe porous solid body by vaporizing the water in the chamber. A coolingplate above the porous solid body condenses the evaporated water thatthen drips onto the porous body and into the pore of the porous solidbody, thus partially saturating the pores of the porous solid body.However, the method of introducing water in this example is one ofseveral ways that water can be delivered. For example, the water canalso be heated and sprayed.

Meanwhile, carbon dioxide as a reactant is pumped into the chamber, andthe carbon dioxide diffuses into the partially saturated pores of theporous body. Once in the pores, the carbon dioxide dissolves in thewater, thus allowing the reaction between the precursor particles andthe carbon dioxide to transform the peripheral portions of the precursorparticles into the first and second layers.

As the reaction between the second reactant and the first layerprogresses, the second reactant continues to react with the first layer,transforming the peripheral portion of the first layer into the secondlayer. The formation of the second layer may be by the exo-solution of acomponent in the first layer, and such a second layer may be a gradientlayer, wherein the concentration of one of the chemical elements(cations) making up the second layer varies from high to low as you movefrom the core particle surface to the end of the first layer. It is alsopossible that the second layer can be a gradient composition as well,such as when the layers are either amorphous or made up of solidsolutions that have either constant or varying compositions.

The presence of the second layer at the periphery the precursor coreeventually hinders further reaction by separating the second reactantand the first layer, causing the reaction to effectively stop, leaving abonding element having the core, the first layer at a periphery of thecore and a second layer on the first layer. The resulting bondingelement is generally larger in size than the original precursorparticle, thereby filling in the surrounding porous regions of theporous solid body and bonding with adjacent materials of the poroussolid body. As a result, the method allows for net-shape formation ofproducts having substantially the same shape as but a higher densitythan the original porous solid body. This is an advantage overtraditionally sintering processes that cause shrinkage from masstransport to produce a higher density material than the initial powdercompact.

C3. Infiltration Medium

The infiltration medium used for transportation into at least a portionof the porous matrix includes a solvent (e.g., water) and a reactivespecies (e.g., CO₂). The solvent can be aqueous or non-aqueous. Thesolvent can include one or more components. For example, in someembodiments, the solvent can be water and ethanol, ethanol and toluene,or mixtures of various ionic liquids, such as ionic liquids based onalkyl-substituted imidazolium and pyridinium cations, with halide ortrihalogenoaluminate anions. Wetting systems are preferred overnon-wetting in order to simplify processing equipment.

The solvent should not be chemically reactive with the porous matrix,although the solvent may chemically react with reactive species. Thesolvent can be removed via a variety of separation methods such as bulkflow, evaporation, sublimation or dissolution with a washing medium, orany other suitable separation method known to one of ordinary skill inthe art.

More specifically, the solvent is a liquid at the temperature where thedissolved reactive species react with the porous matrix. Thistemperature will vary depending on the specific solvent and reactivespecies chosen. Low temperatures are preferred over higher ones to saveenergy and simplify processing equipment thereby reducing manufacturingcosts.

The role of the solvent contrasts with prior art involving reactivesystems, such as, for example, Portland cement, where a solvent such aswater reacts with a porous matrix to form products that contain solventmolecules, such as metal hydrates or metal hydroxides, among otherprecipitation products.

Regardless of the phase of the pure reactive species, the reactivespecies dissolve in the solvent as neutral, anionic or cationic species.For example, the at least one reactive species can be CO₂, which is agas at room temperature that can dissolve in water as neutral CO₂ butcan create reactive species such as H₃O⁺, HCO₃ ⁻, H₂CO₃ and CO₃ ²⁻.Regardless of the initial phase of the reactive species and the solventin the natural state, the infiltration medium is in a liquid phases inthe pores (e.g., interstitial spaces) of a porous matrix.

For example, capillary forces can be used to wick the infiltrationmedium into a porous matrix spontaneously. This type of wetting occurswhen the infiltration medium has a very low contact angle (e.g., <90°C.). In this case, the medium can partially fill (partially saturate) orfully fill (saturate) the pores. The infiltration can also take place insuch a manner that the some pores are filled while others are emptyand/or partially filled. It is also possible that an infiltrated porousmatrix with gradients in pore filling or saturation can be latertransformed to one that is uniform via capillary flow. In addition,wetting does not spontaneously occur when the contact angle of theinfiltration medium is high (e.g.,)>90°. In such cases, fluids will notinfiltrate the porous matrix unless external pressure is applied. Thisapproach has utility when it is desirable to withdraw the infiltrationmedium by the release of pressure (e.g., a reaction can be initiated orhalted by pressure).

When infiltration is done using spontaneous capillary flow in the pores,the bulk flow ceases when the pores are filled (saturated). During HLPS,the reactive species react with the matrix to form one or more productsby the various reactions. The at least one reaction species is depletedfrom inside the pore space and thus need to be replenished during thecourse of the reaction. When pores are fully saturated with theinfiltration medium, the reactive species must be transported from theinfiltration medium external to the porous matrix through the matrixpores. In a quiescent fluid, diffusion is the process by which transporttakes place. Thus, for some HLPS methods whose reactions inside thepores are fast relative to all other mass transport processes, thereaction becomes limited by large increases in the porous matrixthickness. In such a case, only the outer portion of the matrix reactsextensively with the reactive species, while inner regions of the porousmatrix are either less completely reacted or unreacted. This type ofreactions is suitable for preparation of gradient microstructures wherethe concentrations of products of the HLPS process are higher on theoutside portion (near external surface regions) versus the interior ofthe structure.

C4. Process Selection and Control

When highly exothermic reactions proceed slowly relative to transport ofthe infiltration medium and the matrix is thermally insulating,entrapped heat can increase the rate of reaction in the interior of thematrix to enable its interior to contain more product phase (i.e., theproduct of the reaction between the at least one reactive species and aportion of the porous matrix) than its interior. For HLPS processeswhere reactions isothermally proceed at an intermediate rate relative tomass transport of the infiltration medium, diffusion can continue tosupply the pores with reactive species and no gradient in the degree ofreaction (or product concentration) will be observed. In such a case,there is little difference in the chemical and/or phase composition fromthe interior to the exterior of the material of the monolithic structureor body.

In many cases, a uniform microstructure with respect to phase andcomposition is desirable in the monolithic structure body. Furthermore,it is also desirable to conduct HLPS reactions in a relatively shorttime frame, for example, where large thick monolithic bodies arerequired for applications such as for roads or bridges. It is desirableto balance the rate of reaction and mass transport for HLPS processes.The strategy for precursor choice and method of introducing theprecursors to comprise the infiltration medium is important. Thepreferred choice of precursors and method of introducing theinfiltration medium is at least in part a function of the samplethickness in the thinnest direction, the time scale consideredacceptable for the process and the thermodynamic and kinetic constraintsneeded for the process to be commercially viable, such as temperature,pressure and composition.

Table 3 summarizes the precursor choice and method of introductionstrategies. The porous matrix can be directly infiltrated or the porousmatrix may be evacuated prior to any of the infiltration sequencesdescribed in the Table 3. Methods are described that use gases asprecursors, liquids as precursors or solids as precursors. In addition,phase mixtures such as solid and liquids, gases and liquids and gas andsolids can all be used. For example, a reactant such as CO₂ is a gas inits pure state but is converted to a solution species dissolved intowater. Such an event can come about by gaseous diffusion into the porousmatrix and subsequent condensation when a pore is encountered. This typeof precursor system is relevant when microstructures having carbonatephases are desired. The order of addition of the precursors (solvent andreactive species) can influence the reaction yield and microstructure ofthe material.

TABLE 3 Precursors and Methods of Introduction Deli- Methods ofIntroduction Reactive quescent (Reverse/different order may SystemSpecies Solvent Material be applied where appropriate) (1) Gas GasPre-mixing (parallel introduction) two gases and introducing them to alower temperature to condense one or more gas species in the matrix tocomprise an infiltrating solution containing reactive species andsolvent or condense the gas mixture in the matrix by cooling the matrix;or Gases can also be introduced in series where one gas is condensedprior to infiltration or after infiltration and the other is introducedafterwards to dissolve in the liquid phase. (2) Gas Gas Solid Pre-mixingdeliquescent solid with matrix, pre-mix gases (parallel introduction)then flow and/or diffuse the gas mixture through the matrix to forminfiltrating solution; or Gases can be introduced in series into thedeliquescent solid-matrix pre-mixture. The preferred order is to havethe gas that liquefies the deliquescent solid and then the gas thatdissolves to form reactive species. (3) Gas Liquid Solid Pre-mixingdeliquescent solid with matrix, then infiltrate with liquid solvent,followed by adding gas (or visa-versa) to form infiltrating solution inmatrix pores; or Gas and liquid can be pre-mixed as a solution forintroduction into the deliquescent solid-matrix pre-mixture but reactionyield might be reduced. (4) Liquid Liquid Pre-mixing (parallelintroduction) fluids then infiltrate matrix; or Infiltrate fluidsthrough matrix in series with preferred ordering being liquid solventprior to liquid that provides reactive species. (5) Liquid Liquid SolidPre-mixing of deliquescent solid with matrix, then add liquid solvent todissolve deliquescent solid, followed by adding liquid reactive species(or visa-versa) to form infiltrating solution; or Pre-mixing solvent andreactive species in liquid phases as an infiltration solution forintroduction into the deliquescent solid-matrix pre-mixture (6) LiquidGas Infiltrating matrix with gas and condense in matrix as liquid, theninfiltrating second liquid into matrix to mix with first liquid inmatrix; or Preferred route is premixing of gas and liquid by condensinggas and mixing into second liquid, then introduce solution to a porousmatrix (7) Gas Liquid — Infiltrating liquid followed by introducing gas;or Pre-dissolving gas in liquid followed by infiltrating (8) Solid SolidMixing solids with porous matrix, then pressurizing or heating to forminfiltration liquid. One solid may flux the other to form a liquid phasethat can be removed later by washing. Other solids can be added toreduce melting temperature to form liquid phase as long as it can beremoved later. (9) Liquid Solid Preparing infiltration solution bydissolving solid in liquid, followed by infiltration; or Pre-mixingsolid with porous matrix, then infiltrate with liquid (10) Solid LiquidPreparing infiltration solution by dissolving solid in liquid, theninfiltrate; or Pre-mixing solid with porous matrix, then infiltrate withliquid

In some embodiments, the solvent and reactive species may be premixed toform the infiltration medium and then introduced into the matrix in asingle step. In other embodiments, it may be preferable to employmultiple infiltration sequences. For example, the solvent precursorcould be introduced first followed by infiltration of the reactivespecies or vice versa.

Neither the solvent nor the reactive species precursors need to be thesame phase initially as the infiltrating medium will be a liquid that isfound in the pores of the matrix. For example, the solvent precursor canbe a vapor such as water, which is gaseous at temperatures at 100° C. orhigher at atmospheric pressure and can be condensed to a liquid bycooling the matrix to a temperature lower than 100° C. or utilizingsurface energy by using porous matrices with pore sizes in the Kelvinpore-size range (less than 100 nm). When the pores are large, thetemperature is elevated such that gaseous species cannot be thermallycondensed, small amounts of infiltrating solution are needed or otherreasons not discussed here, and it may be desirable to form the liquidin the pore using a deliquescent compound. Examples of such compoundsinclude boric acid, iron nitrate, and potassium hydroxide. In this case,a vapor such as water can convert the deliquescent solid phase in thepore to a liquid and crystal growth of the product phase can proceed inthe pore. This is particularly useful when liquid infiltration anddiffusion limits the thickness of the product made by HLPS.Alternatively, gaseous diffusion can be used to transport species overmuch large distances to form the infiltration medium required for HLPSinside of the pores of the matrix.

Various additives can be incorporated to improve the HLPS process andthe resulting products. Additives can be solids, liquids or gases intheir pure state but either soluble in the solvent phase or co-processed(e.g., pre-mixed) with the porous matrix prior to incorporation of theinfiltration medium. Examples include nucleation catalysts, nucleationinhibition agents, solvent conditioners (e.g., water softening agents),wetting agents, non-wetting agents, cement or concrete additives,additives for building materials, crystal morphology control additives,crystal growth catalysts, additives that slow down crystal growth, pHbuffers, ionic strength adjusters, dispersants, binders, rheologicalcontrol agents, reaction rate catalysts, electrostatic, steric,electrosteric, polyelectrolyte and Vold-layer dispersants, cappingagents, coupling agents and other surface-adsorptive species, acid orbase pH modifiers, additives generating gas, liquids or solids (e.g.,when heated, pressurized, depressurized, reacted with another species orexposed to any processing variable no listed here), and biological orsynthetic components (e.g., serving any of the above functions and/or asa solvent, reactive species or porous matrix).

In some embodiments, a deliquescent solid may be used. The deliquescentsolid may be premixed with the porous matrix. Then pre-mixture of thesolvent and at least one reactive species can be introduced to thedeliquescent solid-porous matrix. The solvent and at least one reactivespecies in the pre-mixture can be both in the gaseous phase or both inliquid phases. In some embodiments, the solvent may be a liquid and theat least one reactive species may be in a gaseous phase in thepre-mixture or vice versa.

A gas-water vapor stream can be passed over a deliquescent salt in theporous matrix to generate the infiltrating medium in a liquid phase inthe interstitial space in the porous matrix. For example, a humidgas-water vapor stream can serve as a solvent for CO₂ dissolution andionization. A large number of salts are known to be deliquescent and canbe used suitable for forming liquid solutions from the flow of humid airover the salt surfaces. Selection of the appropriate salt relies on thelevel of humidity in the air. Some salts can operate at very lowrelative humidity. Examples of deliquescent slats include Mg(NO₃)₂,CaCl₂ and NaCl.

Regarding delivery of the infiltration medium, it can be delivered as abulk solution that spontaneously wets the porous matrix. There are manyoptions for delivery of this solution. First, the porous matrix can beimmersed in the liquid. Second the infiltration solution can be sprayedonto the porous matrix. In a quiescent system, when there is a volume ofinfiltration solution that is greater than the pore volume of the porousmatrix, diffusion propagates the reaction by delivering the reactivespecies to the pore sites.

Alternatively, the fluid can flow (mechanically convected) through theporous matrix by a variety of methods. Methods such as pressurized flow,drying, electro-osmotic flow, magneto-osmosis flow, and temperature- andchemical-gradient-driven flow can be used to flow the liquidinfiltration medium through the porous body. This dynamic flow allowsfresh reactant to be near the porous matrix, as opposed to relying ondiffusional processes. This approach is beneficial as long as the poresize distribution of the matrix permits a reasonably high flow rate of afluid that supplies reactive species faster than a diffusional processand is optimal when the supply rate equals or exceeds the reaction ratefor product formation. In addition, flow-through of the infiltrationmedium is especially useful for highly exothermic reactions. This isparticularly beneficial for monolithic structures that are thick and cangenerate heat internally capable of generating internal pressurescapable of fracturing the monolithic structure.

There are many applications where thicknesses of materials exceed thislength scale. In these cases, mechanical convection of the fluid by anysuitable means known to one of skill in the art is preferred. Analternative is to introduce the solvent or reactive species as a gaseousspecies. Also, supercritical conditions can be employed to achievetransport rates that lie between liquids and gases. Gas species may bemechanically convected by applying a pressure gradient across the porousmatrix. If the gas is a reactive species, pores filled with solventfluid can flow out of the pores leaving behind a film of solvent on thepores that can absorb the reactive species gas. Alternatively, partiallyfilled pores will allow gas to flow through the pores as the solventabsorbs a portion of the gas flowing through.

A system may utilize low temperatures and low pressures to enable a lowcost process. Thus, processes that retain a fraction of solvent in thepores to facilitate gaseous diffusion of reactive species are preferredover those that utilize quiescent fluids for reactions where a largefraction of product is desired. There are many apparatus designs thatcan effectively transport reactant and solvent species to the pores.Some of these designs involve conventional reactor equipment such asfilter presses, spray chambers, autoclaves and steamers.

D. CO₂ Curing Chambers

The invention provides apparatus and methods for low cost, energyefficient and low carbon footprint curing of concretes which utilizecarbon dioxide as a reactant. We now describe the engineering designprinciples and methods that provide carbon capture and utilization withminimal to no cost increase as compared to traditional Portland cementconcrete curing chambers.

D1. Concrete Curing Using CO₂

The systems and methods of the invention are employed using materialsand chemistries that rely on the presence of CO₂ for curing, such as CO₂in a reaction medium such as water, in which carbonic acid, carbonateions, and bi-carbonate ions is provided. Examples of such materials andchemistries have been described hereinabove.

The CO₂ concrete curing process described herein is generally similar tothe conventional concrete curing process described above, with thesignificant difference that five parameters are independently controlledin the controlled curing environment versus the original two describe intraditional curing. In addition to temperature and humidity, the systempressure, the concentration of carbon dioxide, and the gas velocitywithin the chamber are also controlled. A distinction regarding thehumidity control is that in the conventional prior art systems, humidityis raised above ambient because water is a reagent in the curing ofPortland cement, while in the systems and methods according to thepresent invention, water is not a reagent but rather is a reactionmedium. Rather, in the present systems and methods CO₂ is the reagent.Accordingly, is the present invention, water vapor, temperature and gasvelocity may be controlled to cause water to be either removed from thecuring product or added to the curing product as may be required Both“big room” and “multi-lane” type curing systems as described inconventional concrete curing systems may also be utilized in CO2 curingsystems.

FIG. 5 is a schematic diagram of a CO₂ concrete curing chamberconstructed and operated according to principles of the invention. InFIG. 5 a curing chamber is supplied with CO₂ from a source by way of aproportioning valve, which can control the pressure, the flow rate, andthe duration of flow of the CO₂. The CO₂ atmosphere is recirculatedthrough a blower and a heat exchanger or heater, so that the temperatureof the atmosphere within the curing chamber can be regulated ormodified. In some embodiments, a heat exchanger can be used to cool theatmosphere within the curing chamber, for example if the curing reactionis sufficiently exothermic that the atmosphere is being heatedexcessively.

In the embodiments described, industrial grade CO₂ at about 99% purityis used, which is provided by a variety of different industrial gascompanies, such as Praxair, Inc., Linde AG, Air Liquide, and others.This supply can be held in large pressurized holding tanks in the formof liquid carbon dioxide regulated at specific temperature such that itmaintains a vapor pressure of approximately 300 PSIG. This gas is thenpiped and pressure regulated to a CO₂ curing chamber. Alternatively, CO₂captured at industrial facilities (including but not limited to ammoniaproduction plants, natural gas processing plants, cement manufacturingplants, glass manufacturing plants, CO₂ from landfills and otherbiogases, biodiesel plants) and combustion source facilities (e.g.,electric power or steam production) can be used. In addition, CO₂produced from carbon dioxide production wells that drill in the earth toextract a carbon dioxide stream from a geologic formation or group offormations which contain deposits of carbon dioxide can also be used.

D2. CO₂ Concrete Curing Temperature Controls

In some embodiments, temperature is measured utilizing a sensor such asa thermocouple or an RTD. The measurement signal is directed back to acontroller or computer that is able to regulate energy into the heatexchanger and thereby adjust the temperature of the entire system overtime. The blower is an important component of the heating system as itis able to help transfer the heat energy to the gas which transfers tothe products and the chamber itself which is an important part ofcontrolled moisture of the samples. The method of heating can beelectric or gas fired. Jacket heaters may be utilized to control thetemperature of the CO₂ that flows through a chamber in contact with theheating jacket, any convenient source of heat can be used. The means ofexternal heating may include but are not limited to electric heating,hot water heating, or hot oil heating. For CO₂ curing chambers indirectgas fired systems have been utilized thus far and direct fired gasburners have been avoided because they will pull air and products ofcombustion into the system, thereby diluting the CO₂ and making controlof the CO₂ concentration problematic. Some smaller scale systems such asthe Drum Reactors utilize electric jacket heaters to heat the entiresurface of the chamber rather than a heating element within the chamber.

D3. CO₂ Concrete Curing Humidity Control Options

FIG. 6 is a schematic diagram of a CO₂ concrete curing chamber thatprovides humidification according to principles of the invention. InFIG. 6, a water supply is provided and water vapor is added to theatmosphere that is circulating within the curing chamber. The water canbe any convenient source of potable water. In some embodiments, ordinarytap water is used. In some embodiments, the water can be converted tovapor by flowing through a misting nozzle or an atomizing spray nozzle,an electric vapor generator, a gas fired vapor generator, or by beingheated above the gas temperature in the chamber so as to causeevaporation from a liquid water supply an example being a drum reactorwith an immersion heater. In yet another embodiment, the CO₂ supply canbe flowed into the systems after having been bubbled through a heatedwater supply in order to increase relative humidity of the incoming gasstream an example being a drum reactor configured for “flow through” or“open loop” processing.

Relative humidity is an important parameter in both traditional concretecuring as well as in CO₂ concrete curing. In a traditional curingchamber a moist air atmosphere exists that is comprised of mostlynitrogen, oxygen, and water vapor. In these systems relative humidity ismost often measured by a standard capacitive sensor technology. However,CO₂ curing chambers have a gas atmosphere comprised predominately ofcarbon dioxide that is incompatible with some types of these sensors.Sensing technology such as dry-bulb wet-bulb techniques that utilize thepsychrometric ratios for carbon dioxide and water vapor or dipolepolarization water vapor measurement instruments or chilled mirrorhygrometers or capacitive humidity sensors in the CO₂ concrete curingsystems described herein.

Depending on the type and geometry of the product being cured, thedesign of the chamber, and the packing efficiency of product in thechamber the humidity may need to be either decreased or increased andregulated to a specified set point. Set points may range anywhere from1% to 99% relative humidity. Three different methods for humiditycontrol may exist in CO₂ concrete curing processes that could becombined into a single system. The method for humidification in oneembodiment of a CO₂ curing system is represented in FIG. 6.

FIG. 7 is a schematic diagram of a CO₂ curing chamber that providesdehumidifcation by purging humid gas according to principles of theinvention. As mentioned, in some cases it is necessary to removemoisture from the system to cure the concrete products with CO₂. Asimple method of reducing the relative humidity is by displacing thehumid gas in the system with a dry gas, in this case carbon dioxide. Thehumid CO₂ gas mixture is released via an exhaust valve that could be aproportioning control valve or an automatic bleed valve, and make up dryCO₂ enters the recirculating system so as to decrease the relativehumidity to the desired set point while maintaining the regulatedpressure and gas flow within the curing system. In this type of purgingdehumidification, a disadvantage is that a greater amount of carbondioxide will be exhausted from the system. However, an advantage is thatthe amount of water vapor can be driven down to the concentration ofwater vapor in the incoming purge gas, which is some instances can beextremely low if the CO₂ purge gas is generated by vaporization ofliquid CO₂.

FIG. 8 is a schematic diagram of a CO₂ curing chamber that providesdehumidifcation using a chilled heat exchanger according to principlesof the invention. In an alternative embodiment, the dehumidificationapparatus and method shown in FIG. 8 represents a technique to reducerelative humidity and therefore remove water vapor from the gas by anon-purging method. This particular technique uses a water extractionapparatus and method to remove the water, which in one preferredembodiment is a chilled heat exchanger. A recirculating chiller unitcirculates a water and ethylene glycol solution chilled down between −15C and 15 C through a high surface area stainless steel heat exchangercoil that is mounted in the direct line of humid gas flow. Some waterfrom the gas stream will undergo a phase transition and condense to forma liquid on the coil, which can then be collected and drained out of thesystem via a liquid drain trap, conventional valve, or a solenoid valveon a timer to drain the liquid and not the gas. The benefit of usingthis type of system is that during the process a very minimal amount ofcarbon dioxide gas will be ejected and wasted as compared to the purgingdehumidification method shown in FIG. 7. One disadvantage of thistechnique is the need for some extra equipment that is not standard intraditional concrete curing chambers. Another disadvantage is that theenergy demand of the system will increase to operate the chiller unit.

In some situations, for example if there is a need to remove a largeamount of water from the system, the two dehumidification methodsmentioned above may be operated together to keep humidity levels as lowas possible.

D4. Filling and Concentration Ramp Up of Carbon Dioxide in the CuringSystem

At the start of a curing process, a pre carbon dioxide dwell period withcontrol of parameters such as temperature, relative humidity, and gasvelocity may first exist, at which point carbon dioxide concentrationsmay be increased in a curing chamber by flowing CO₂ into the system fromthe gas source and displacing air out of the chamber, which is calledthe purging cycle. Throughout the purging cycle an excess of carbondioxide will be used which accounts for some small yet unavoidable wastein the process. In some embodiments, it is expected that the exiting gascan be collected and fractionated to recover the CO₂ that wouldotherwise be lost by venting or by being transferred to a secondarycuring chamber or an additional bay in a multi-lane curing system. Thepurging cycle is concluded when the desired concentration of CO₂ in thecuring chamber is reached. The concentration of CO₂ can be measuredutilizing a variety of different measurement techniques such asnon-dispersive infrared sensing or gas chromatography. Reaction rates inthe carbonating cement compositions described hereinabove have a strongrelationship to carbon dioxide concentration, and therefore typicallyhigh CO₂ concentrations are reached at the beginning of the reactioncycle, but this does not have to be the case in all instances. After thepurging cycle, the relative humidity, temperature, and gas velocity inthe chamber can be adjusted to reduce the evaporation of water from thespecimens in the chamber if required.

In the embodiments described herein, carbon dioxide is a reactant andwill be consumed in the process. Therefore it is important to replenishthe supply of CO₂ throughout the process so as to maintain a desiredrate of reaction. After the high flow of CO₂ into the chamber in thepurge cycle has concluded, a few options exist to maintain a high levelof CO₂ during the reaction.

D5. CO₂ Replenishment by Constant Flow and Bleed (Open Loop)

One technique that can be applied is to utilize a consistent yet lowflow of CO₂ throughout the entire duration of the curing process whilebleeding out a low flow of exhaust gas. This type of curing system canbe of the simplest and require the minimum amount of feedback andcontrol from system and be utilized when a profile is not yet known fora product or when precise control is not required. However, it may alsobe configured in a sophisticated manner that could have flow meters onthe inlet and outlet of the system to conduct a mass balance of CO₂ anddetermine the rates and total amounts of CO₂ sequestered using acomputerized control system which could ultimately indicate reactionrates and determine when the curing process has completed. This willallow CO₂ concentrations to be replenished. The flow rate of the make upCO₂ need only be as high as the rate of gas consumed in the process. Thesecondary effect of this method is a “purging dehumidification” asdescribed earlier by using the dry gas to carry away the moist gas. Thisprocess can be implemented by providing a high flow CO₂ valve for thepurging cycle and a low flow CO₂ valve or flow controller for thereplenishment throughout the duration of the curing cycle, asillustrated in FIG. 9. As described earlier, this methodology for CO₂replenishment and dehumidification require CO₂ in excess of what isrequired in the reaction.

This constant flow methodology is called flow through reacting, and isalso useful for processes utilizing continuous CO₂-rich gas wastestreams. Such waste streams could be flue gasses from a variety ofindustries including but not limited to cement kilns, glass meltingkilns, power plants, biogases, and the like. Therefore, such constantflow chambers can be configured and compatible with both an industrialCO₂ gas supply as well as waste gas streams. Solidia Drum Reactors shownin FIG. 12 through FIG. 15 are an example of a small scale unit that canbe utilized as a low flow CO₂ replenishment system.

D6. Low Pressure Regulated Replenishment

After the CO₂ purging cycling there is another method to maintain CO₂concentrations throughout the duration of the curing cycle. Thisalternative method uses low pressure regulation. In a mechanicallyregulated system a low pressure diaphragm regulator is used. Thisregulator can control pressures to as low as 1 inch of H₂O (orapproximately 1/400 of an atmosphere). These regulators are highlysensitive and allow for replenishment of CO₂ only as the pressure isdecreased due to the consumption of CO₂ in the reaction process. Anexample of this type of system is the Solidia small scale Drum Reactorthat can be configured for low pressure regulated replenishment as wellas constant flow replenishment.

In another embodiment, an electronic approach can be used by measuringthe pressure in the system with a highly accurate low pressuretransducer coupled with a proportioning control valve instead of amechanical diaphragm valve. FIG. 10 is a schematic diagram of a curingchamber that has a CO₂ purge line and that can provide regulatedpressure CO₂ replenishment using this technique. An example of this isthe Solidia autoclave system operated at low pressure.

D7. CO₂ Concentration Closed Loop Regulation

Another method for sustaining carbon dioxide concentrations during thereaction is well suited for keeping a highly consistent concentration,although it is the most expensive technique. This method uses themeasurement of CO₂ concentration in the system directly, and employs acontroller such as a PLC to control the CO₂ concentration at a set pointwith an electronic/automated control valve. A measurement technique tomeasure CO₂ directly such as NDIR should preferably be employed. In theNDIR measurement method, a gas sample stream is pulled from the systemvia a low flow pump. A chiller is used to drop moisture out of the gasstream before it is sampled by the NDIR instrument. Therefore themeasurement provided by the analyzer is missing the water vaporcomponent of the gas stream and needs be adjusted to account for thehumidity that has been removed from the test sample. A measurement ofthe humidity in the system gas flow can be performed using a drybulb-wet bulb psychrometric technique, as illustrated in FIG. 19 (seedry bulb-wet bulb humidity measurement device 1930) or using a differenttype of moisture sensor. The true CO₂ concentration can be calculatedusing the computer control system or PLC. Once the true CO₂concentration is known, the actuated proportioning control valve can adddry CO₂ into the system when it has been consumed and has gone below theset point that is desired at that time. In various embodiments, the setpoint can vary with time, if necessary, based on experience in curingspecific compositions, shape and sizes of concrete specimens.

FIG. 11 is a schematic diagram of a midsized curing chamber withmultiple methods of humidity control as well as ability to control andreplenish CO₂ using constant flow or pressure regulation and that cancontrol humidity according to principles of the invention.

D8. Gas Velocity Control

Another important control parameter is gas velocity across the materialthat is to be cured in the system which can be very dependent on numberof different aspects including but not limited to chamber design, baffledesign, fan size, fan speed/power, number of fans, temperature gradientwithin the system, rack design within the system, and sample geometrywithin the system. The simplest method to control the gas velocitywithin the chamber is by adjusting the blower speed (RPM's), typicallydone by utilization of a variable frequency drive to allow for controlof the blower motor speed. The blower can be used to circulate gas at adesired velocity in the curing chamber. Gas velocity in the system ismeasured in the system via a variety of different techniques includingbut not limited to pitot tubes measurement and laser Doppler detectionsystems. The measurement signal for gas velocity can be sent back to acomputer system or programmable logic controller and be utilized as acontrol parameter in the curing profile.

APPARATUS EXAMPLES

FIG. 12 through FIG. 20 show various embodiments of apparata that areconstructed and that operate according to the description of theinventive systems given herein.

FIG. 12 is an image of several drum reactors constructed from 55 gallonstainless steel drums.

FIG. 13 is an image of the interior of a drum reactor including racks tosupport pallets of materials to be processed therein.

FIG. 14 is an image of the exterior of a drum reactor surrounded by aheating jacket, and showing several thermocouple connectors and a gasentry port.

FIG. 15 is an image of a control panel for a drum reactor showing fourcontrollers that control (from left to right) an immersion heater, ajacket heater, an inline gas heater, and a fan, with readouts for thetemperatures of the three heaters.

FIG. 16 is an image of a commercially available CDS curing chamber(available from CDS Inc., Cinderhill Trading Estate, Weston Coyney Road,Longton, Stoke-on-Trent ST3 5JU, Great Britain) which has beenretrofitted for low pressure CO₂ curing according to principles of theinvention. In FIG. 16 a CO₂ inlet 1610 from a source of CO₂ such as atank into the chamber has been added and is illustrated. This is anexample of a CO₂ concentration regulated curing system called theSolidia Portable Shipping Container Reactor.

FIG. 17 is an image of a portion of the interior of the chamber of FIG.16, showing further modifications made to the prior art Portland cementcuring system. A Dipole Polarization Moisture Volume Probe 1710 has beenadded. A commercially available CO₂ nondispersive infrared (NDIR)analyzer 1740 that permits the determination of the CO₂ concentrationhas been added (Siemens Ultramat 23, available from Siemens AG, OneInternet Plaza, Johnson City, Tenn. 37604). A sample chiller 1730 hasbeen added in the flow line that enters this analyzer. The samplechiller drops moisture out of the gas stream first so the sensor canread the CO₂ concentration with no interference from water vapor. Thechiller 1730 can be used to condense water in the system and todehumidify the gas stream that is provided to the system. A CO₂proportioning control valve 1720 has been added, which is used to forramp up the CO₂ concentration and then sustain the CO₂ levels throughoutthe course of the curing reaction.

FIG. 18 is another view of the CO₂ NDIR analyzer 1740.

FIG. 19 is a view within the curing chamber that illustrates additionalcomponents that have been added. A dipole polarization gas sampler 1910that is used to measure percent H₂O by volume with extremely highaccuracy has been added. A condensing coil 1920 is added in the suctionside of the CO₂ return duct, before the circulating gas reaches a blowerand a 50 kW electric heater. The water vapor recovered as liquid fromthe chiller inside the return duct is extracted by a condensate drainfor dehumidification of the flowing CO₂ gas and can be measured via aflow meter to enable measurement of drying rate of specimens in thechamber. A dry bulb-wet bulb humidity measurement device 1930 was added,which is similar to a sling psychrometer in operation. The temperaturedifferential between the wet bulb thermometer and the dry bulbthermometer provides a measure of the relative humidity. In oneembodiment, a programmable logic controller (PLC) is programmed withinstructions that provide a calculate relative humidity based on thethermal measurements, the psychrometric ratio of the gasses, and anequation that represents a steam in the range of temperature beingutilized. The curing chamber is modified by providing an aperture 1940through which gas is sampled at a rate of 1 L/min for analysis in theCO₂ NDIR analyzer 1740 (located outside the active portion of the curingchamber). In the example shown in FIG. 19, an inlet 1950 for the CO₂ gascoming from a proportioning valve is provided in the bottom of thecuring chamber. In other embodiments, the inlet can be located onanother face of the chamber, or multiple inlets could be used.

FIG. 20 is a screen shot of the display connected to a programmablelogic controller or other control apparatus, such as a general purposeprogrammable computer that operates under the control of a set ofinstructions recorded on a machine-readable medium. In the embodimentshown, the curing chamber is a pressure vessel that is operated as anatmospheric pressure reactor, using approximately 0.25 PSIG overpressureof 50-99% pure CO₂ that is taken as boil-off from a vessel that containsliquid CO₂ at high pressure and the remainder mostly water vapor. Theautomated control system screen, which can be a touchscreen, shows avariety of controls and read outs of process variables such as time,temperature, relative humidity, pressure, gas flow rates and so forth.The automated control system provides control of the temperature andhumidity profile in the presence of high CO₂ gas concentration. When thecuring chamber is first loaded and started, a CO₂ purge system is usedto bring in CO₂ over the course of 15 minutes, during which time theambient air in the curing chamber is displaced by CO₂. The systems ofthe invention provide dynamic control in which temperature, humidity,CO₂ concentration, CO₂ flow rate, and system pressure are independentlycontrolled throughout the cure cycle, and each can be varied so as to beincreased or decreased independently or dependently of the changes inthe other variables. The controller can record any of the data that itdisplays.

CURING METHOD EXAMPLES Example 1 6-Inch by 9-Inch Pavers Cured in a DrumReactor in a CO₂ Atmosphere with Self-Generated Humidity

Raw Materials

Synthetic Wollastonite (SC-C2), Donghai Golden Resources Industries,Donghai, China; ¼″ trap rock aggregate from Stavola (NJ), constructionsand from Bound Brook (NJ) and Glenium 7500 (BASF). Table 4 gives themixture proportion of the raw material used to prepare the pavers.

TABLE 4 Mixing Proportions (100 kg batch size) Solid Components: 94.3%Synthetic Wollastonite (SC-C2)  18% 17.1 kg Construction sand 55.2% 52.2kg ¼″ aggregate 26.8% 25 kg Liquid Components:  5.7% Tap Water 98.81% 5.632 kg Glenium 7500 1.19% 0.068 kgMixing Procedure

-   -   1. Measure and load 25 kg of ¼″ aggregate into a planetary mixer        (Sicoma™ MP375/250).    -   2. Measure and load 55.2 kg of construction sand into the mixer.    -   3. Measure and load 17.1 kg of Synthetic Wollastonite (SC-C2)        mixer.    -   4. Mix the solid components loaded into the mixer for        approximately 3 minutes. This creates a dry mixture.    -   5. Measure and load the liquid component (5.632 kg of water and        0.068 kg of Glenium 7500 as in this example) into the mixer        containing the dry mixture, and continue mixing for        approximately for 2 minutes until uniform slurry is formed. This        creates a wet mixture.        Pressing Procedure    -   1. The wet mixture is discharged into a hopper and conveyed to        the paver forming machine (Columbia Model 1600)    -   2. The wet mixture is then discharged into the feed hopper of        the paver forming machine    -   3. The wet mixture is then discharged from the feed hopper into        the paver mold cavity. As the wet mixture is discharged into the        paver mold cavity, the mold is vibrated so as to effectively        fill the cavity.    -   4. The compression head of the paver press compresses the wet        mixture for approximately 1.5 seconds or until the wet mixture        reaches a height of 2⅝″ inch. This creates a green ceramic body.    -   5. The green ceramic body in the shape of a paver is then        stripped from the mold cavity.        Curing Procedure

Green ceramic bodies in the shape of pavers are cured in the drumreactor as follows. The 1.6 kW commercially available heating jacket incontact with the exterior of a 55 gallon stainless steel drum is heatedup to a 110 degrees Celsius to preheat the shell for approximatelytwenty minutes. Green ceramic bodies are loaded onto aluminum sheets andplaced into the shelving of system that contains a 373 CFM fan and abaffle system to direct the flow across the samples. The lid thatcontains a ½″ diameter orifice is sealed around the drum via acompression gasket ring. The fan is started, and a flow ranging from200-500 L/min of CO₂ is initiated, flowing through the system andexiting the ½″ orifice on the lid. After fifteen minutes, the flow ofCO₂ is stopped and the ½″ orifice is plugged with a low pressure relieffitting, exhausting any pressure that exceeds ½ PSIG. The heating jacketis controlled to regulate an internal gas temperature of the system at60 C. As pressure builds from expansion of gasses during heat up andwater vapor pressure build up from evaporation of water in samples, thelow pressure relief fitting will intermittently relieve pressure andexhaust some humid CO₂. An alternative CO2 line is opened that containsa low pressure regulator that regulated gas in the drum reactor to 0.33PSIG. This regulator adds gas to the system if the pressure drops below0.33 PSIG, which occurs once thermal equilibrium has been reached andCO₂ is being consumed in the reaction chamber. The relative humidity inthe system is sustained at a relative high amount, in the area of60-96%. After 20 hours, the flow of gas into the system is stopped andthe lid is opened. The green ceramic bodies, now converted to curedpavers, are removed from the system and contain anywhere from 3-5% CO₂by mass, and have compressive strengths in the range of 2,000-13,000 PSIas tested per the ASTM C 936.

Example 2 6-Inch by 9-Inch Pavers Cured in a Drum Reactor in a CO2Atmosphere with Condensate Drainage for Dehumidification

Green ceramic bodies in the shape of pavers are prepared in the samemanner as Example 1.

Curing Procedure

The curing process described in Example 1 is carried out while utilizinga solenoid valve on a timer (opens for 5 seconds every 10 minutes) atthe bottom of the drum reactor as to remove condensate on the bottom ofthe reactor and therefore reduce humidity in the system over the courseof the cure cycle. A time is used such that the system stays sealed andonly intermittently bleeds condensate without bleeding very much gas outof the system. Liquid drain traps may be used but can be challenging touse due to the low gas pressures involved. During this the relativehumidity is maintained in the area of 37-67%. After 20 hours, the flowof gas into the system is stopped and the lid is opened. The curedpavers are removed from the system and contain anywhere from 3-5% CO₂ bymass, and have compressive strengths in the range of 2,000-13,000 PSI astested per the ASTM C 936.

Example 3 6-Inch by 9-Inch Pavers Cured in a Drum Reactor in a CO2Atmosphere with Added Humidity by Heating Water on the Bottom of theChamber

Green ceramic bodies in the shape of pavers are prepared in the samemanner as Example 1.

The curing process described in Example 1 is carried out wherein thebottom of the drum reactor equipped with a 1 kW immersion heater locatedat the bottom of the drum. The drum is filled with approximately 3-5gallons of water, enough to cover the 1 kW immersion heater. The lidthat contains a ½″ diameter orifice is sealed around the drum via acompression gasket ring. The fan is started, and a flow ranging from200-500 L/min of CO₂ is initiated, flowing through the system andexiting the ½″ orifice on the lid. After ten minutes, the flow of CO₂ isstopped and the ½″ orifice is plugged with a low pressure relieffitting, exhausting any pressure that exceeds ½ PSIG. The heating jacketis controlled to regulate an internal gas temperature of the system at60 C. To increase relative humidity in the system the power output tothe immersion heater is controlled to heat the water to 64 C that ismeasured by a separate thermocouple immersed in the water. As pressurebuilds from expansion of gasses during heat up and water vapor pressurebuild up from evaporation of water in samples, the low pressure relieffitting will intermittently relieve pressure and exhaust some humid CO₂.An alternative CO2 line is opened that contains a low pressure regulatorthat regulated gas in the drum reactor to 0.33 PSIG. This regulator addsgas to the system if the pressure drops below 0.33 PSIG, which occursonce thermal equilibrium has been reached and CO₂ is being consumed inthe reaction chamber. The relative humidity in the system is sustainedat a very high amount, in the area of 83-99%. After 20 hours, the flowof gas into the system is stopped and the lid is opened. The pavers areremoved from the system and contain anywhere from 3-5% CO₂ by mass, andhave compressive strengths in the range of 5,000-13,000 PSI as testedper the ASTM C 936.

Example 4 6-Inch by 9-Inch Pavers Cured in a Drum Reactor in a CO2Atmosphere with a Humidified Incoming CO₂ Stream by Bubbling the GasStream Through a Hot Water System

Green ceramic bodies in the shape of pavers are prepared in the samemanner as Example 1.

Curing Procedure

Samples are cured in a flow-through drum reactor as follows: The 1.6 kwcommercially available heating jacket in contact with the exterior of a55 gallon stainless steel drum is heated up to 110 Celsius to preheatthe shell for approximately twenty minutes. Samples are loaded ontoaluminum sheets and placed into the shelving system that contains a 373CFM fan and a baffle system to direct the flow across the samples. Thelid that contains a ½″ diameter orifice is sealed around the drum via acompression gasket ring. For this experiment, a dilute CO₂ stream iscreated. A 99.9% industrial food grade CO2 gas stream and compressed airare regulated using a mixing gas rotameter that allow the flow of eachgas to be controlled and CO2 concentrations diluted down to the range of25-40% with a total flow rate ranging between 20-50 L/min. Acommercially available 1.1 kw heated steamer pressure vessel (pressurecooker) is filled with water and connected to the CO₂ inlet. The gasstream is bubbled through the regulated 75 C hot water and into the drumreactor, providing a highly humidified gas stream. The water temperaturemay be controlled to adjust the humidity. The lines running from hotsteamer to the drum reactor are insulated as to prevent condensation andmay also be heat traced for an even higher humidity. The fan is startedand a flow is started through the system, exiting the ½″ orifice on thelid. A constant exhaust of this humid gas mixture exits the systems viathe ½″ orifice on the front cover over the course of the curing cycle.The heating jacket is controlled to regulate an internal gas temperatureof the system at 60 C and keep the walls of systems warm as to preventcondensation of the incoming humidified gas stream. The relativehumidity of the system is sustained at a relatively high amount, in thearea of 92-98%. After 20 hours, the flow of gas into the system isstopped and the lid is opened.

Example 5 Lightweight Block with 18% Ground Calcium Silicate Cured in anAutoclave at Atmospheric Pressure in a CO₂ Atmosphere Utilizing aChiller to Reduce Humidity

Raw Materials

Synthetic Wollastonite (SC-C2), Donghai Golden Resources Industries,Donghai, China; ½″ trap rock aggregate from Stavola (N.J.), constructionsand from Bound Brook (N.J.), Bottom ash from Austral Masonry(Australia), crusher dust from Austral Masonry (Australia), SikaViscocrete (Sika) and Glenium 7500 (BASF). Table 5 shows the mixtureproportion of the raw material used to prepare the pavers.

TABLE 5 Mixing Proportions (100 kg batch size) Solid Components 92.61%Synthetic Wollastonite (SC-C2)   18% 16.67 kg Construction Sand 25.20%23.33 kg ¼″ Aggregate 16.10% 14.91 kg Bottom ash 19.50% 18.06 kg CrusherDust 21.20% 19.63 kg Liquid Components  7.31% Tap Water 99.30% 7.26 kgGlenium 7500  0.30% 0.02 kg Sika Viscocrete  0.40% 0.03 kgMixing Procedure

-   -   1. Measure and load 23.33 kg of construction sand into a        planetary mixer (Sicoma™ MP375/250).    -   2. Measure and load 14.91 kg of ½″ aggregate into the mixer.    -   3. Measure and load 18.06 kg of bottom ash into the mixer    -   4. Measure and load 19.63 kg of crusher dust into the mixer    -   5. Measure and load 16.67 kg of Synthetic Wollastonite (SC-C2)        mixer.    -   6. Mix the solid components loaded into the mixer for        approximately 3 minutes. This creates a dry mixture.    -   7. Measure and load the liquid component (7.26 kg of water, 0.02        kg of Glenium 7500 and 0.068 kg of Glenium 7500 as in this        example) into the mixer containing the dry mixture, and continue        mixing for approximately for 2 minutes until uniform slurry is        formed. This creates a wet mixture.        Pressing Procedure    -   1. The wet mixture is discharged into a hopper and conveyed to        the paver forming machine (Columbia Model 1600)    -   2. The wet mixture is then discharged into the feed hopper of        the paver forming machine    -   3. The wet mixture is then discharged from the feed hopper into        the paver mold cavity. As the wet mixture is discharged into the        paver mold cavity, the mold is vibrated so as to effectively        fill the cavity.    -   4. The compression head of the paver press compresses the wet        mixture for approximately 1.5 seconds or until the wet mixture        reaches a height of 2⅝″ inch. This creates a green ceramic body.    -   5. The green ceramic body in the shape of a block is then        stripped from the mold cavity.        Curing Procedure

Green ceramic bodies in the shape of blocks are formed 3 at a time perboard. Each board is placed on an aluminum cart and transferred insideof a 7 ft diameter, 12 ft long, horizontal, autoclave, which had beenpre-heated to 60° C. via an indirect steam heat exchanger coil with 140PSI of steam pressure. The autoclave was then purged with CO₂ gas heatedto 75° C. by keeping the top gas vent open while running a 7.5horsepower blower at 3600 RPM's while flowing 60 PSI of CO2 gas pressurefrom a liquid CO2 holding tank into the chamber. The purge is conductedfor 12 minutes to reach a CO2 concentration of 97% by volume. Thebleed-valve at the top of the autoclave was then closed, and the CO₂pressure within the autoclave was regulated to 0 psig and temperature ofthe gas maintained at 60 C. In this embodiment the relative humidity isnot precisely controlled but is adjusted manually. For the first 5 hoursof the profile, a high surface area heat exchanger chilled to 4 C withan Ethylene Glycol/Water mixture via a 10 kW chiller is exposed to thegas stream allowing the chamber atmosphere to be dehumidified for thisduration. The condensate water formed on the chiller is dripped down anddropped out of the reactor via a commercially available Armstrong LiquidDrain Trap. After 5 hours the chiller is turned off and the humidity inthe system begins to rise and sustain within a range of 60 and 55%. Atthe end of the 20 hour curing cycle fresh ambient air is brought intothe curing system via a pump and displaces the CO2 from the curingchamber for safe opening of the chamber door. Upon completion of thecuring cycle some amount of condensed water from had accumulated at thebottom of the system, accounting or a majority of the water lost fromthe blocks.

FIG. 21 is the corresponding temperature and humidity profile for theexample 5.

Example 6 Normal Weight Block Cured in Autoclave at Atmospheric Pressurein a CO₂ Atmosphere Utilizing Self-Generated Humidity

Raw Materials:

Synthetic Wollastonite (SC-C2), Donghai Golden Resources Industries,Donghai, China; ¼″ trap rock aggregate from Stavola (NJ), constructionsand from Bound Brook (N.J.) and Glenium 7500 (BASF). Table 6 shows themixing proportion of the raw material used for this example.

TABLE 6 Mixing Proportions (100 kg batch size) Solid Components: 93.9%Synthetic Wollastonite (SC-C2)  18% 16.902 kg Construction Sand 55.2%51.832 kg ¼″ Aggregate 26.8% 25.165 kg Liquid Components:  6.1% TapWater 98.81%  6.02 kg Glenium 7500 1.19% 0.08 kgMixing Procedure

The mixing procedure is similar to the procedure adopted for pressedpavers as described in Example 1.

Pressing Procedure

Similar procedure was used to press blocks as mentioned in Example 1 forpressed pavers with an exception in the mold geometry to form the greenceramic body. The dimension of the pressed blocks were 7⅝″×7⅝″×15⅝″ (49%of volume being solid).

Curing Procedure

Green ceramic bodies in the form of blocks are formed 3 at a time perboard. Each board is placed on an aluminum cart and transferred insideof a 7 ft diameter, 12 ft long, horizontal, autoclave, which had beenpre-heated to 60° C. via an indirect steam heat exchanger coil with 140PSI of steam pressure. The autoclave was then purged with CO₂ gas heatedto 75° C. by keeping the top gas vent open while running a 7.5horsepower blower at 3600 RPM's while flowing 60 PSI of CO2 gas pressurefrom a liquid CO2 holding tank into the chamber. The purge is conductedfor 12 minutes to reach a CO2 concentration of 97% by volume. Thebleed-valve at the top of the autoclave was then closed, and the CO₂pressure within the autoclave was regulated to 0 psig and temperature ofthe gas maintained at 60 C. Over the course of the 8 hour curing cycle,the relative humidity naturally increases up to approximately 70% dueevaporation of water from the samples and tend to slowly taper off toapproximately 65% due to condensation in the system. At the end of the 8hour curing cycle fresh ambient air is brought into the curing systemvia a pump and displaces the CO2 from the curing chamber for safeopening of the chamber door. Upon completion of the curing cycle someamount of condensed water from had accumulated at the bottom of thesystem, accounting or a majority of the water lost from the blocks.

FIG. 22 is the corresponding temperature and humidity profile for theexample 6.

Testing

The cured ceramic body in form of pressed block was tested forunconfined compressive strength as per ASTM C90. The compressivestrength of the blocks prepared was 17.2 MPa (2500 psi).

DEFINITIONS

As used herein, the terms “chemical reagent,” “reagent,” “reactant,” and“chemical reactant” are all intended to be synonymous, and are used torefer to a chemical species that reacts with another chemical species.

Recording the results from an operation or data acquisition, such as forexample, recording results at a particular time or under particularoperating conditions, is understood to mean and is defined herein aswriting output data in a non-volatile manner to a storage element, to amachine-readable storage medium, or to a storage device. Non-volatilemachine-readable storage media that can be used in the invention includeelectronic, magnetic and/or optical storage media, such as magneticfloppy disks and hard disks; a DVD drive, a CD drive that in someembodiments can employ DVD disks, any of CD-ROM disks (i.e., read-onlyoptical storage disks), CD-R disks (i.e., write-once, read-many opticalstorage disks), and CD-RW disks (i.e., rewriteable optical storagedisks); and electronic storage media, such as RAM, ROM, EPROM, CompactFlash cards, PCMCIA cards, or alternatively SD or SDIO memory; and theelectronic components (e.g., floppy disk drive, DVD drive, CD/CD-R/CD-RWdrive, or Compact Flash/PCMCIA/SD adapter) that accommodate and readfrom and/or write to the storage media. Unless otherwise explicitlyrecited, any reference herein to “record” or “recording” is understoodto refer to a non-volatile record or a non-volatile recording.

As is known to those of skill in the machine-readable storage mediaarts, new media and formats for data storage are continually beingdevised, and any convenient, commercially available storage medium andcorresponding read/write device that may become available in the futureis likely to be appropriate for use, especially if it provides any of agreater storage capacity, a higher access speed, a smaller size, and alower cost per bit of stored information. Well known oldermachine-readable media are also available for use under certainconditions, such as punched paper tape or cards, magnetic recording ontape or wire, optical or magnetic reading of printed characters (e.g.,OCR and magnetically encoded symbols) and machine-readable symbols suchas one and two dimensional bar codes. Recording image data for later use(e.g., writing an image to memory or to digital memory) can be performedto enable the use of the recorded information as output, as data fordisplay to a user, or as data to be made available for later use. Suchdigital memory elements or chips can be standalone memory devices, orcan be incorporated within a device of interest. “Writing output data”or “writing an image to memory” is defined herein as including writingtransformed data to registers within a microcomputer.

“Microcomputer” is defined herein as synonymous with microprocessor,microcontroller, and digital signal processor (“DSP”). It is understoodthat memory used by the microcomputer, including for exampleinstructions for data processing coded as “firmware” can reside inmemory physically inside of a microcomputer chip or in memory externalto the microcomputer or in a combination of internal and externalmemory. Similarly, analog signals can be digitized by a standaloneanalog to digital converter (“ADC”) or one or more ADCs or multiplexedADC channels can reside within a microcomputer package. It is alsounderstood that field programmable array (“FPGA”) chips or applicationspecific integrated circuits (“ASIC”) chips can perform microcomputerfunctions, either in hardware logic, software emulation of amicrocomputer, or by a combination of the two. Apparatus having any ofthe inventive features described herein can operate entirely on onemicrocomputer or can include more than one microcomputer.

General purpose programmable computers useful for controllinginstrumentation, recording signals and analyzing signals or dataaccording to the present description can be any of a personal computer(PC), a microprocessor based computer, a portable computer, or othertype of processing device. The general purpose programmable computertypically comprises a central processing unit, a storage or memory unitthat can record and read information and programs using machine-readablestorage media, a communication terminal such as a wired communicationdevice or a wireless communication device, an output device such as adisplay terminal, and an input device such as a keyboard. The displayterminal can be a touch screen display, in which case it can function asboth a display device and an input device. Different and/or additionalinput devices can be present such as a pointing device, such as a mouseor a joystick, and different or additional output devices can be presentsuch as an enunciator, for example a speaker, a second display, or aprinter. The computer can run any one of a variety of operating systems,such as for example, any one of several versions of Windows, or ofMacOS, or of UNIX, or of Linux. Computational results obtained in theoperation of the general purpose computer can be stored for later use,and/or can be displayed to a user. At the very least, eachmicroprocessor-based general purpose computer has registers that storethe results of each computational step within the microprocessor, whichresults are then commonly stored in cache memory for later use, so thatthe result can be displayed, recorded to a non-volatile memory, or usedin further data processing or analysis.

In this specification and the appended claims, the singular forms “a,”“an,” and “the” include plural reference, unless the context clearlydictates otherwise.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art. Although any methods and materials similar or equivalent tothose described herein can also be used in the practice or testing ofthe present disclosure, the preferred methods and materials are nowdescribed. Methods recited herein may be carried out in any order thatis logically possible, in addition to a particular order disclosed.

INCORPORATION BY REFERENCE

References and citations to other documents, such as patents, patentapplications, patent publications, journals, books, papers, webcontents, have been made in this disclosure. All such documents arehereby incorporated herein by reference in their entirety for allpurposes. Any material, or portion thereof, that is said to beincorporated by reference herein, but which conflicts with existingdefinitions, statements, or other disclosure material explicitly setforth herein is only incorporated to the extent that no conflict arisesbetween that incorporated material and the present disclosure material.In the event of a conflict, the conflict is to be resolved in favor ofthe present disclosure as the preferred disclosure.

EQUIVALENTS

The representative examples disclosed herein are intended to helpillustrate the invention, and are not intended to, nor should they beconstrued to, limit the scope of the invention. Indeed, variousmodifications of the invention and many further embodiments thereof, inaddition to those shown and described herein, will become apparent tothose skilled in the art from the full contents of this document,including the examples and the references to the scientific and patentliterature cited herein. The examples contain important additionalinformation, exemplification and guidance that can be adapted to thepractice of this invention in its various embodiments and equivalentsthereof.

What is claimed is:
 1. A curing system for curing a material whichrequires CO₂ as a curing reagent, comprising: a curing chamberconfigured to contain a material that consumes CO₂ as a reagent and thatdoes not cure in the absence of CO₂ during curing, said curing chamberhaving at least one port configured to allow said material to beintroduced into said curing chamber and to be removed from said curingchamber, and having at least one closure for said port, said closureconfigured to provide an atmospheric seal when closed so as to preventcontamination of a gas present in said curing chamber by gas outsidesaid curing chamber; a source of carbon dioxide configured to providegaseous carbon dioxide to said curing chamber by way of a gas entry portin said curing chamber, said source of carbon dioxide having at leastone flow regulation device configured to control a flow rate of saidgaseous carbon dioxide into said curing chamber; a gas flow subsystemconfigured to circulate said gas through said curing chamber during atime period when said material that consumes CO₂ as a reagent is beingcured; a temperature control subsystem configured to control atemperature of said gas within said chamber; a humidity controlsubsystem configured to control a humidity in said gas within saidchamber; and at least one controller in communication with at least oneof said source of carbon dioxide, said gas flow subsystem, saidtemperature control subsystem, and said humidity control subsystem, saidat least one controller configured to control independently during atime period when said material that consumes CO₂ as a reagent is beingcured at least a respective one of said flow rate of said gaseous carbondioxide, said circulation of said gas through said curing chamber, saidtemperature of said gas, and said humidity in said gas.
 2. The curingsystem of claim 1, wherein said curing chamber is configured to containa pressure of gas therein that is above atmospheric pressure.
 3. Thecuring system of claim 1, wherein said at least one flow regulationdevice comprises at least one of a pressure regulator and a flowcontroller configured to supply carbon dioxide gas at a ratesubstantially equal to a rate of consumption of said carbon dioxide bysaid material that consumes CO₂ as a reagent during curing.
 4. Thecuring system of claim 1, wherein said at least one flow regulationdevice comprises at least one of a pressure regulator and a flowcontroller configured to supply carbon dioxide gas at a rate sufficientto purge ambient atmosphere from said curing chamber in a time periodbetween 2-120 minutes to achieve a target CO₂ concentration in a rangeof 50-90% by volume.
 5. The curing system of claim 1, wherein said atleast one flow regulation device comprises at least one of a pressureregulator and a flow controller configured to supply carbon dioxide gasat a rate substantially equal to a rate of venting of said gas from saidcuring chamber.
 6. The curing system of claim 1, wherein said gas flowsubsystem includes a measurement apparatus configured to measure anamount of carbon dioxide in said gas present in said curing chamber. 7.The curing system of claim 1, wherein said gas flow subsystem includes ameasurement apparatus configured to measure a gas velocity of said gaspresent in said curing chamber.
 8. The curing system of claim 7, whereinsaid measurement apparatus configured to measure a gas velocity is aselected one of a pitot tube, an orifice plate, an anemometer, and alaser Doppler detection system.
 9. The curing system of claim 1, whereinsaid gas flow subsystem includes a variable speed blower configured tocirculate gas at a desired velocity in said curing chamber.
 10. Thecuring system of claim 1, wherein said temperature control subsystemincludes a temperature sensor configured to measure said temperature ofsaid gas in said curing chamber.
 11. The curing system of claim 1,wherein said temperature control subsystem includes a heat exchanger toregulate said temperature of said gas in said curing chamber.
 12. Thecuring system of claim 1, wherein said temperature control subsystemincludes a heat exchanger to control a temperature of said gaseouscarbon dioxide provided to said curing chamber by way of said gas entryport in said curing chamber.
 13. The curing system of claim 1, whereinsaid temperature control subsystem includes a heater situated on anexternal surface or built into walls of said curing chamber.
 14. Thecuring system of claim 1, wherein said humidity control subsystemincludes a measurement apparatus configured to determine a relativehumidity of said gas within said chamber.
 15. The curing system of claim1, wherein said humidity control subsystem includes a condenserconfigured to reduce said humidity in said gas within said chamber. 16.The curing system of claim 1, wherein said humidity control subsystemincludes an exhaust valve configured to reduce said humidity in said gaswithin said chamber.
 17. The curing system of claim 1, wherein saidhumidity control subsystem includes a water supply configured toincrease said humidity in said gas within said chamber.
 18. The curingsystem of claim 1, wherein said at least one controller is a selectedone of a programmable logic controller, a controller having a touchscreen display, and a general purpose programmable computer thatoperates under the control of a set of instructions recorded on amachine-readable medium.
 19. The curing system of claim 1, wherein saidat least one controller includes a display configured to display to auser any of a duration of a curing cycle, said flow rate of said gaseouscarbon dioxide, a concentration of carbon dioxide in said curingchamber, a rate of circulation of said gas through said curing chamber,said temperature of said gas, and said humidity in said gas.
 20. Thecuring system of claim 1, wherein said at least one controller isconfigured to record any of a duration of a curing cycle, said flow rateof said gaseous carbon dioxide, a concentration of carbon dioxide insaid curing chamber, a rate of circulation of said gas through saidcuring chamber, said temperature of said gas, and said humidity in saidgas.